Fix handling NULL context pointers in ExceptionTracker::UpdateNonvolatileRegisters
Fix handling NULL context pointers in ExceptionTracker::UpdateNonvolatileRegisters

This change fixes handling of NULL context pointers in ExceptionTracker::UpdateNonvolatileRegisters
on OSX where the NULL value of a context pointer indicates that the unwinder doesn't know the
context pointer.

bitcrazed/coreclr,ytechie/coreclr,Alcaro/coreclr,blackdwarf/coreclr,roncain/coreclr,jhendrixMSFT/coreclr,andschwa/coreclr,sergey-raevskiy/coreclr,ytechie/coreclr,mocsy/coreclr,jakesays/coreclr,SlavaRa/coreclr,apanda/coreclr,mskvortsov/coreclr,lzcj4/coreclr,mocsy/coreclr,ramarag/coreclr,wkchoy74/coreclr,josteink/coreclr,misterzik/coreclr,matthubin/coreclr,rartemev/coreclr,martinwoodward/coreclr,dasMulli/coreclr,sejongoh/coreclr,schellap/coreclr,ytechie/coreclr,mskvortsov/coreclr,russellhadley/coreclr,bartdesmet/coreclr,tijoytom/coreclr,ericeil/coreclr,benpye/coreclr,ktos/coreclr,DasAllFolks/coreclr,sjsinju/coreclr,apanda/coreclr,dasMulli/coreclr,Dmitry-Me/coreclr,naamunds/coreclr,MCGPPeters/coreclr,krixalis/coreclr,matthubin/coreclr,alexperovich/coreclr,qiudesong/coreclr,gkhanna79/coreclr,taylorjonl/coreclr,yeaicc/coreclr,jakesays/coreclr,cshung/coreclr,parjong/coreclr,fffej/coreclr,blackdwarf/coreclr,AlfredoMS/coreclr,hanu412/coreclr,Alcaro/coreclr,matthubin/coreclr,fffej/coreclr,cmckinsey/coreclr,fffej/coreclr,parjong/coreclr,gitchomik/coreclr,botaberg/coreclr,ytechie/coreclr,chrishaly/coreclr,chuck-mitchell/coreclr,James-Ko/coreclr,mskvortsov/coreclr,hseok-oh/coreclr,kyulee1/coreclr,AlfredoMS/coreclr,taylorjonl/coreclr,YongseopKim/coreclr,mokchhya/coreclr,Djuffin/coreclr,bartonjs/coreclr,alexperovich/coreclr,fieryorc/coreclr,Godin/coreclr,LLITCHEV/coreclr,Samana/coreclr,ganeshran/coreclr,hseok-oh/coreclr,cshung/coreclr,parjong/coreclr,sergey-raevskiy/coreclr,martinwoodward/coreclr,YongseopKim/coreclr,sperling/coreclr,Lucrecious/coreclr,grokys/coreclr,DasAllFolks/coreclr,AlfredoMS/coreclr,sperling/coreclr,LLITCHEV/coreclr,taylorjonl/coreclr,James-Ko/coreclr,sperling/coreclr,neurospeech/coreclr,misterzik/coreclr,mocsy/coreclr,wateret/coreclr,geertdoornbos/coreclr,wateret/coreclr,gkhanna79/coreclr,sperling/coreclr,josteink/coreclr,parjong/coreclr,zmaruo/coreclr,sjsinju/coreclr,chenxizhang/coreclr,yeaicc/coreclr,grokys/coreclr,mmitche/coreclr,dkorolev/coreclr,geertdoornbos/coreclr,ericeil/coreclr,russellhadley/coreclr,mokchhya/coreclr,poizan42/coreclr,DasAllFolks/coreclr,qiudesong/coreclr,libengu/coreclr,wateret/coreclr,wtgodbe/coreclr,DasAllFolks/coreclr,fffej/coreclr,Samana/coreclr,mskvortsov/coreclr,qiudesong/coreclr,bartonjs/coreclr,ZhichengZhu/coreclr,fernando-rodriguez/coreclr,GuilhermeSa/coreclr,jakesays/coreclr,swgillespie/coreclr,orthoxerox/coreclr,orthoxerox/coreclr,hseok-oh/coreclr,ktos/coreclr,ZhichengZhu/coreclr,sergey-raevskiy/coreclr,bartonjs/coreclr,sjsinju/coreclr,LLITCHEV/coreclr,dasMulli/coreclr,rartemev/coreclr,roncain/coreclr,parjong/coreclr,david-mitchell/coreclr,serenabenny/coreclr,russellhadley/coreclr,schellap/coreclr,dasMulli/coreclr,swgillespie/coreclr,chuck-mitchell/coreclr,jhendrixMSFT/coreclr,Sridhar-MS/coreclr,botaberg/coreclr,Djuffin/coreclr,Alcaro/coreclr,gkhanna79/coreclr,krk/coreclr,stormleoxia/coreclr,YongseopKim/coreclr,Sridhar-MS/coreclr,ragmani/coreclr,bjjones/coreclr,blackdwarf/coreclr,bartdesmet/coreclr,ramarag/coreclr,xoofx/coreclr,chrishaly/coreclr,fernando-rodriguez/coreclr,bartdesmet/coreclr,shana/coreclr,mocsy/coreclr,hseok-oh/coreclr,ruben-ayrapetyan/coreclr,fieryorc/coreclr,hanu412/coreclr,neurospeech/coreclr,iamjasonp/coreclr,kyulee1/coreclr,ktos/coreclr,manu-silicon/coreclr,yizhang82/coreclr,Djuffin/coreclr,lzcj4/coreclr,alexperovich/coreclr,jakesays/coreclr,ruben-ayrapetyan/coreclr,andschwa/coreclr,ytechie/coreclr,rartemev/coreclr,richardlford/coreclr,botaberg/coreclr,Godin/coreclr,geertdoornbos/coreclr,ktos/coreclr,sagood/coreclr,serenabenny/coreclr,krk/coreclr,geertdoornbos/coreclr,chenxizhang/coreclr,sergey-raevskiy/coreclr,krk/coreclr,richardlford/coreclr,wtgodbe/coreclr,apanda/coreclr,bartdesmet/coreclr,blackdwarf/coreclr,poizan42/coreclr,pgavlin/coreclr,bartonjs/coreclr,dasMulli/coreclr,sagood/coreclr,perfectphase/coreclr,vinnyrom/coreclr,xtypebee/coreclr,xtypebee/coreclr,chaos7theory/coreclr,pgavlin/coreclr,KrzysztofCwalina/coreclr,ramarag/coreclr,DasAllFolks/coreclr,ragmani/coreclr,bitcrazed/coreclr,dasMulli/coreclr,ragmani/coreclr,serenabenny/coreclr,dkorolev/coreclr,yeaicc/coreclr,geertdoornbos/coreclr,gkhanna79/coreclr,blackdwarf/coreclr,bartdesmet/coreclr,wateret/coreclr,misterzik/coreclr,yeaicc/coreclr,schellap/coreclr,rartemev/coreclr,tijoytom/coreclr,jakesays/coreclr,bjjones/coreclr,perfectphase/coreclr,kyulee1/coreclr,jamesqo/coreclr,JonHanna/coreclr,SpotLabsNET/coreclr,dpodder/coreclr,sagood/coreclr,mokchhya/coreclr,botaberg/coreclr,perfectphase/coreclr,taylorjonl/coreclr,Samana/coreclr,OryJuVog/coreclr,russellhadley/coreclr,cydhaselton/coreclr,apanda/coreclr,krytarowski/coreclr,mmitche/coreclr,gitchomik/coreclr,Godin/coreclr,LLITCHEV/coreclr,bitcrazed/coreclr,Djuffin/coreclr,dpodder/coreclr,shahid-pk/coreclr,mskvortsov/coreclr,poizan42/coreclr,dkorolev/coreclr,shahid-pk/coreclr,ramarag/coreclr,OryJuVog/coreclr,david-mitchell/coreclr,KrzysztofCwalina/coreclr,shana/coreclr,stormleoxia/coreclr,roncain/coreclr,mokchhya/coreclr,qiudesong/coreclr,misterzik/coreclr,krk/coreclr,cydhaselton/coreclr,josteink/coreclr,naamunds/coreclr,KrzysztofCwalina/coreclr,chaos7theory/coreclr,blackdwarf/coreclr,LLITCHEV/coreclr,ericeil/coreclr,jhendrixMSFT/coreclr,libengu/coreclr,DickvdBrink/coreclr,schellap/coreclr,martinwoodward/coreclr,stormleoxia/coreclr,JosephTremoulet/coreclr,kyulee1/coreclr,david-mitchell/coreclr,Dmitry-Me/coreclr,david-mitchell/coreclr,tijoytom/coreclr,chrishaly/coreclr,sejongoh/coreclr,shana/coreclr,grokys/coreclr,manu-silicon/coreclr,sejongoh/coreclr,poizan42/coreclr,chenxizhang/coreclr,mocsy/coreclr,taylorjonl/coreclr,ZhichengZhu/coreclr,chaos7theory/coreclr,xoofx/coreclr,SlavaRa/coreclr,jamesqo/coreclr,Dmitry-Me/coreclr,chaos7theory/coreclr,pgavlin/coreclr,grokys/coreclr,James-Ko/coreclr,AlexGhiondea/coreclr,matthubin/coreclr,Dmitry-Me/coreclr,gitchomik/coreclr,Dmitry-Me/coreclr,swgillespie/coreclr,gkhanna79/coreclr,libengu/coreclr,naamunds/coreclr,russellhadley/coreclr,wkchoy74/coreclr,jhendrixMSFT/coreclr,Djuffin/coreclr,Samana/coreclr,wtgodbe/coreclr,KrzysztofCwalina/coreclr,sjsinju/coreclr,sperling/coreclr,ganeshran/coreclr,dpodder/coreclr,ganeshran/coreclr,libengu/coreclr,parjong/coreclr,JosephTremoulet/coreclr,bjjones/coreclr,chuck-mitchell/coreclr,cmckinsey/coreclr,mmitche/coreclr,vinnyrom/coreclr,russellhadley/coreclr,misterzik/coreclr,krixalis/coreclr,chrishaly/coreclr,schellap/coreclr,benpye/coreclr,ragmani/coreclr,fieryorc/coreclr,dpodder/coreclr,wateret/coreclr,neurospeech/coreclr,KrzysztofCwalina/coreclr,DickvdBrink/coreclr,sperling/coreclr,rartemev/coreclr,SpotLabsNET/coreclr,xtypebee/coreclr,chuck-mitchell/coreclr,Godin/coreclr,yizhang82/coreclr,sjsinju/coreclr,misterzik/coreclr,neurospeech/coreclr,sagood/coreclr,Sridhar-MS/coreclr,cydhaselton/coreclr,cshung/coreclr,swgillespie/coreclr,dasMulli/coreclr,ganeshran/coreclr,iamjasonp/coreclr,wkchoy74/coreclr,orthoxerox/coreclr,andschwa/coreclr,ragmani/coreclr,orthoxerox/coreclr,geertdoornbos/coreclr,KrzysztofCwalina/coreclr,krk/coreclr,shahid-pk/coreclr,stormleoxia/coreclr,perfectphase/coreclr,cydhaselton/coreclr,yizhang82/coreclr,GuilhermeSa/coreclr,qiudesong/coreclr,jamesqo/coreclr,bartdesmet/coreclr,jhendrixMSFT/coreclr,fffej/coreclr,krytarowski/coreclr,josteink/coreclr,Godin/coreclr,fffej/coreclr,ZhichengZhu/coreclr,sergey-raevskiy/coreclr,sejongoh/coreclr,DasAllFolks/coreclr,AlexGhiondea/coreclr,bjjones/coreclr,pgavlin/coreclr,krixalis/coreclr,stormleoxia/coreclr,tijoytom/coreclr,sejongoh/coreclr,ZhichengZhu/coreclr,neurospeech/coreclr,yizhang82/coreclr,martinwoodward/coreclr,fieryorc/coreclr,LLITCHEV/coreclr,ktos/coreclr,SpotLabsNET/coreclr,mmitche/coreclr,wtgodbe/coreclr,dpodder/coreclr,chenxizhang/coreclr,ericeil/coreclr,ericeil/coreclr,ytechie/coreclr,gitchomik/coreclr,wtgodbe/coreclr,krytarowski/coreclr,spoiledsport/coreclr,YongseopKim/coreclr,hanu412/coreclr,YongseopKim/coreclr,MCGPPeters/coreclr,bitcrazed/coreclr,cshung/coreclr,iamjasonp/coreclr,bitcrazed/coreclr,pgavlin/coreclr,qiudesong/coreclr,benpye/coreclr,wkchoy74/coreclr,AlfredoMS/coreclr,mskvortsov/coreclr,rartemev/coreclr,swgillespie/coreclr,tijoytom/coreclr,libengu/coreclr,alexperovich/coreclr,Sridhar-MS/coreclr,jamesqo/coreclr,James-Ko/coreclr,grokys/coreclr,mmitche/coreclr,JonHanna/coreclr,vinnyrom/coreclr,MCGPPeters/coreclr,AlexGhiondea/coreclr,Alcaro/coreclr,zmaruo/coreclr,orthoxerox/coreclr,mmitche/coreclr,chuck-mitchell/coreclr,bitcrazed/coreclr,serenabenny/coreclr,vinnyrom/coreclr,libengu/coreclr,krytarowski/coreclr,Samana/coreclr,James-Ko/coreclr,DickvdBrink/coreclr,naamunds/coreclr,James-Ko/coreclr,cshung/coreclr,lzcj4/coreclr,andschwa/coreclr,SlavaRa/coreclr,swgillespie/coreclr,ramarag/coreclr,DickvdBrink/coreclr,jamesqo/coreclr,kyulee1/coreclr,ramarag/coreclr,shahid-pk/coreclr,naamunds/coreclr,shana/coreclr,hanu412/coreclr,ktos/coreclr,hanu412/coreclr,wateret/coreclr,wkchoy74/coreclr,bartonjs/coreclr,Dmitry-Me/coreclr,jhendrixMSFT/coreclr,perfectphase/coreclr,LLITCHEV/coreclr,cmckinsey/coreclr,lzcj4/coreclr,GuilhermeSa/coreclr,zmaruo/coreclr,bjjones/coreclr,chenxizhang/coreclr,SlavaRa/coreclr,fernando-rodriguez/coreclr,poizan42/coreclr,ruben-ayrapetyan/coreclr,JonHanna/coreclr,benpye/coreclr,wkchoy74/coreclr,manu-silicon/coreclr,shana/coreclr,martinwoodward/coreclr,shahid-pk/coreclr,yizhang82/coreclr,bartonjs/coreclr,Samana/coreclr,bartonjs/coreclr,taylorjonl/coreclr,lzcj4/coreclr,fieryorc/coreclr,shahid-pk/coreclr,benpye/coreclr,spoiledsport/coreclr,chrishaly/coreclr,OryJuVog/coreclr,geertdoornbos/coreclr,hseok-oh/coreclr,blackdwarf/coreclr,sjsinju/coreclr,cmckinsey/coreclr,mokchhya/coreclr,sergey-raevskiy/coreclr,Alcaro/coreclr,fernando-rodriguez/coreclr,roncain/coreclr,cmckinsey/coreclr,matthubin/coreclr,gkhanna79/coreclr,SpotLabsNET/coreclr,SpotLabsNET/coreclr,AlexGhiondea/coreclr,Sridhar-MS/coreclr,JonHanna/coreclr,cmckinsey/coreclr,Lucrecious/coreclr,xtypebee/coreclr,dpodder/coreclr,JosephTremoulet/coreclr,ganeshran/coreclr,dkorolev/coreclr,krytarowski/coreclr,vinnyrom/coreclr,ruben-ayrapetyan/coreclr,pgavlin/coreclr,JosephTremoulet/coreclr,Sridhar-MS/coreclr,krk/coreclr,chaos7theory/coreclr,YongseopKim/coreclr,chuck-mitchell/coreclr,orthoxerox/coreclr,Dmitry-Me/coreclr,gitchomik/coreclr,iamjasonp/coreclr,jhendrixMSFT/coreclr,chaos7theory/coreclr,alexperovich/coreclr,matthubin/coreclr,botaberg/coreclr,Godin/coreclr,sejongoh/coreclr,stormleoxia/coreclr,DickvdBrink/coreclr,ganeshran/coreclr,xtypebee/coreclr,ZhichengZhu/coreclr,ericeil/coreclr,perfectphase/coreclr,bartdesmet/coreclr,fieryorc/coreclr,AlexGhiondea/coreclr,kyulee1/coreclr,OryJuVog/coreclr,ruben-ayrapetyan/coreclr,vinnyrom/coreclr,manu-silicon/coreclr,bjjones/coreclr,jakesays/coreclr,roncain/coreclr,iamjasonp/coreclr,Godin/coreclr,andschwa/coreclr,dkorolev/coreclr,josteink/coreclr,chenxizhang/coreclr,martinwoodward/coreclr,SlavaRa/coreclr,MCGPPeters/coreclr,andschwa/coreclr,Lucrecious/coreclr,ruben-ayrapetyan/coreclr,botaberg/coreclr,david-mitchell/coreclr,JonHanna/coreclr,grokys/coreclr,xoofx/coreclr,krixalis/coreclr,sagood/coreclr,roncain/coreclr,Lucrecious/coreclr,mokchhya/coreclr,benpye/coreclr,xoofx/coreclr,yeaicc/coreclr,zmaruo/coreclr,hseok-oh/coreclr,serenabenny/coreclr,DickvdBrink/coreclr,schellap/coreclr,OryJuVog/coreclr,spoiledsport/coreclr,ZhichengZhu/coreclr,fernando-rodriguez/coreclr,yizhang82/coreclr,xoofx/coreclr,benpye/coreclr,poizan42/coreclr,roncain/coreclr,shana/coreclr,andschwa/coreclr,manu-silicon/coreclr,SpotLabsNET/coreclr,yeaicc/coreclr,stormleoxia/coreclr,Alcaro/coreclr,JosephTremoulet/coreclr,xtypebee/coreclr,manu-silicon/coreclr,alexperovich/coreclr,wtgodbe/coreclr,schellap/coreclr,chuck-mitchell/coreclr,Lucrecious/coreclr,spoiledsport/coreclr,Djuffin/coreclr,zmaruo/coreclr,SlavaRa/coreclr,GuilhermeSa/coreclr,apanda/coreclr,josteink/coreclr,naamunds/coreclr,swgillespie/coreclr,richardlford/coreclr,taylorjonl/coreclr,KrzysztofCwalina/coreclr,krixalis/coreclr,MCGPPeters/coreclr,AlfredoMS/coreclr,chrishaly/coreclr,manu-silicon/coreclr,richardlford/coreclr,ragmani/coreclr,cshung/coreclr,serenabenny/coreclr,richardlford/coreclr,apanda/coreclr,neurospeech/coreclr,david-mitchell/coreclr,ktos/coreclr,mocsy/coreclr,dkorolev/coreclr,JonHanna/coreclr,cmckinsey/coreclr,MCGPPeters/coreclr,ramarag/coreclr,xoofx/coreclr,JosephTremoulet/coreclr,yeaicc/coreclr,sperling/coreclr,spoiledsport/coreclr,Lucrecious/coreclr,richardlford/coreclr,sagood/coreclr,GuilhermeSa/coreclr,mocsy/coreclr,GuilhermeSa/coreclr,hanu412/coreclr,cydhaselton/coreclr,krytarowski/coreclr,lzcj4/coreclr,tijoytom/coreclr,shahid-pk/coreclr,mokchhya/coreclr,naamunds/coreclr,vinnyrom/coreclr,cydhaselton/coreclr,fernando-rodriguez/coreclr,OryJuVog/coreclr,AlfredoMS/coreclr,jamesqo/coreclr,Lucrecious/coreclr,spoiledsport/coreclr,bitcrazed/coreclr,martinwoodward/coreclr,josteink/coreclr,AlexGhiondea/coreclr,krixalis/coreclr,zmaruo/coreclr,gitchomik/coreclr,sejongoh/coreclr,iamjasonp/coreclr,wkchoy74/coreclr