Fix CharacterData::SubstringData()
Fix CharacterData::SubstringData()

It was not following the spec and it could panic.

nrc/servo,rnestler/servo,ryancanhelpyou/servo,tafia/servo,sadmansk/servo,runarberg/servo,tschneidereit/servo,mdibaiee/servo,RenaudParis/servo,WriterOfAlicrow/servo,rnestler/servo,akosel/servo,samfoo/servo,ConnorGBrewster/servo,hyowon/servo,dhananjay92/servo,hyowon/servo,A-deLuna/servo,SimonSapin/servo,rnestler/servo,huonw/servo,peterjoel/servo,upsuper/servo,eddyb/servo,notriddle/servo,dagnir/servo,saratang/servo,pyfisch/servo,thiagopnts/servo,GreenRecycleBin/servo,mdibaiee/servo,kindersung/servo,jimberlage/servo,peterjoel/servo,vks/servo,mattnenterprise/servo,zentner-kyle/servo,meh/servo,karlito40/servo,thiagopnts/servo,eddyb/servo,hyowon/servo,brendandahl/servo,AnthonyBroadCrawford/servo,rentongzhang/servo,GreenRecycleBin/servo,pyfisch/servo,nnethercote/servo,deokjinkim/servo,ConnorGBrewster/servo,nrc/servo,A-deLuna/servo,samfoo/servo,jlegendary/servo,dagnir/servo,nrc/servo,rixrix/servo,jdramani/servo,evilpie/servo,mbrubeck/servo,szeged/servo,akosel/servo,tempbottle/servo,rnestler/servo,g-k/servo,DominoTree/servo,AnthonyBroadCrawford/servo,boghison/servo,wartman4404/servo,nick-thompson/servo,dhananjay92/servo,codemac/servo,anthgur/servo,sadmansk/servo,saneyuki/servo,walac/servo,s142857/servo,evilpie/servo,meh/servo,youprofit/servo,avadacatavra/servo,aidanhs/servo,jlegendary/servo,jlegendary/servo,youprofit/servo,tafia/servo,boghison/servo,pgonda/servo,saneyuki/servo,tafia/servo,szeged/servo,zhangjunlei26/servo,evilpie/servo,canaltinova/servo,samfoo/servo,GreenRecycleBin/servo,nerith/servo,saneyuki/servo,tempbottle/servo,codemac/servo,GyrosOfWar/servo,aidanhs/servo,rixrix/servo,GyrosOfWar/servo,jlegendary/servo,emilio/servo,larsbergstrom/servo,nnethercote/servo,nerith/servo,akosel/servo,aweinstock314/servo,steveklabnik/servo,anthgur/servo,caldwell/servo,nnethercote/servo,KiChjang/servo,nick-thompson/servo,WriterOfAlicrow/servo,zhangjunlei26/servo,vks/servo,steveklabnik/servo,j3parker/servo,anthgur/servo,dhananjay92/servo,notriddle/servo,paulrouget/servo,pyecs/servo,splav/servo,dhananjay92/servo,aweinstock314/servo,avadacatavra/servo,runarberg/servo,samfoo/servo,mattnenterprise/servo,dsandeephegde/servo,peterjoel/servo,KiChjang/servo,rnestler/servo,emilio/servo,cbrewster/servo,karlito40/servo,jimberlage/servo,wartman4404/servo,thiagopnts/servo,jlegendary/servo,meh/servo,wartman4404/servo,larsbergstrom/servo,A-deLuna/servo,splav/servo,jlegendary/servo,KiChjang/servo,runarberg/servo,fiji-flo/servo,mdibaiee/servo,mbrubeck/servo,RenaudParis/servo,emilio/servo,mt2d2/servo,saneyuki/servo,szeged/servo,nrc/servo,zhangjunlei26/servo,larsbergstrom/servo,DominoTree/servo,mt2d2/servo,youprofit/servo,codemac/servo,larsbergstrom/servo,fiji-flo/servo,emilio/servo,tschneidereit/servo,zhangjunlei26/servo,rnestler/servo,emilio/servo,DominoTree/servo,wartman4404/servo,tempbottle/servo,saratang/servo,aidanhs/servo,nick-thompson/servo,karlito40/servo,notriddle/servo,vks/servo,nnethercote/servo,karlito40/servo,vks/servo,samfoo/servo,aidanhs/servo,paulrouget/servo,mbrubeck/servo,nick-thompson/servo,larsbergstrom/servo,saneyuki/servo,GreenRecycleBin/servo,zhangjunlei26/servo,huonw/servo,tempbottle/servo,SimonSapin/servo,mt2d2/servo,nnethercote/servo,dati91/servo,s142857/servo,nick-thompson/servo,mbrubeck/servo,mattnenterprise/servo,RenaudParis/servo,huonw/servo,canaltinova/servo,nrc/servo,j3parker/servo,eddyb/servo,nrc/servo,GyrosOfWar/servo,nick-thompson/servo,dvberkel/servo,saneyuki/servo,pyecs/servo,cbrewster/servo,GreenRecycleBin/servo,j3parker/servo,mattnenterprise/servo,jgraham/servo,saratang/servo,mbrubeck/servo,peterjoel/servo,dati91/servo,larsbergstrom/servo,avadacatavra/servo,hyowon/servo,akosel/servo,WriterOfAlicrow/servo,wpgallih/servo,splav/servo,pyfisch/servo,ryancanhelpyou/servo,pgonda/servo,nerith/servo,huonw/servo,jgraham/servo,nerith/servo,runarberg/servo,wpgallih/servo,jgraham/servo,WriterOfAlicrow/servo,A-deLuna/servo,youprofit/servo,boghison/servo,notriddle/servo,upsuper/servo,deokjinkim/servo,AnthonyBroadCrawford/servo,KiChjang/servo,paulrouget/servo,splav/servo,bjwbell/servo,A-deLuna/servo,larsbergstrom/servo,eddyb/servo,dati91/servo,peterjoel/servo,eddyb/servo,ConnorGBrewster/servo,tafia/servo,WriterOfAlicrow/servo,DominoTree/servo,GreenRecycleBin/servo,walac/servo,walac/servo,ConnorGBrewster/servo,codemac/servo,splav/servo,mattnenterprise/servo,cbrewster/servo,zhangjunlei26/servo,pyecs/servo,dvberkel/servo,caldwell/servo,kindersung/servo,anthgur/servo,sadmansk/servo,s142857/servo,canaltinova/servo,avadacatavra/servo,tschneidereit/servo,bjwbell/servo,KiChjang/servo,jimberlage/servo,dsandeephegde/servo,mattnenterprise/servo,steveklabnik/servo,CJ8664/servo,akosel/servo,splav/servo,rixrix/servo,zentner-kyle/servo,CJ8664/servo,ryancanhelpyou/servo,KiChjang/servo,DominoTree/servo,brendandahl/servo,szeged/servo,g-k/servo,upsuper/servo,wartman4404/servo,szeged/servo,caldwell/servo,caldwell/servo,aweinstock314/servo,evilpie/servo,akosel/servo,paulrouget/servo,evilpie/servo,pgonda/servo,saratang/servo,codemac/servo,codemac/servo,boghison/servo,rentongzhang/servo,karlito40/servo,tempbottle/servo,dsandeephegde/servo,meh/servo,rentongzhang/servo,dsandeephegde/servo,jdramani/servo,ryancanhelpyou/servo,thiagopnts/servo,thiagopnts/servo,j3parker/servo,pgonda/servo,notriddle/servo,dvberkel/servo,AnthonyBroadCrawford/servo,upsuper/servo,RenaudParis/servo,caldwell/servo,dsandeephegde/servo,RenaudParis/servo,jimberlage/servo,szeged/servo,pyecs/servo,mbrubeck/servo,aidanhs/servo,peterjoel/servo,mt2d2/servo,fiji-flo/servo,dvberkel/servo,runarberg/servo,aweinstock314/servo,rnestler/servo,DominoTree/servo,thiagopnts/servo,pyfisch/servo,jdramani/servo,tafia/servo,emilio/servo,GyrosOfWar/servo,pyecs/servo,j3parker/servo,jimberlage/servo,bjwbell/servo,wpgallih/servo,ConnorGBrewster/servo,kindersung/servo,peterjoel/servo,g-k/servo,wpgallih/servo,GyrosOfWar/servo,wpgallih/servo,larsbergstrom/servo,paulrouget/servo,splav/servo,dvberkel/servo,dsandeephegde/servo,paulrouget/servo,huonw/servo,karlito40/servo,mbrubeck/servo,vks/servo,aidanhs/servo,jdramani/servo,zentner-kyle/servo,avadacatavra/servo,sadmansk/servo,paulrouget/servo,dagnir/servo,upsuper/servo,caldwell/servo,g-k/servo,sadmansk/servo,karlito40/servo,cbrewster/servo,sadmansk/servo,szeged/servo,g-k/servo,aidanhs/servo,dvberkel/servo,saneyuki/servo,wartman4404/servo,cbrewster/servo,mattnenterprise/servo,steveklabnik/servo,A-deLuna/servo,WriterOfAlicrow/servo,brendandahl/servo,GreenRecycleBin/servo,avadacatavra/servo,bjwbell/servo,emilio/servo,canaltinova/servo,A-deLuna/servo,DominoTree/servo,steveklabnik/servo,RenaudParis/servo,nnethercote/servo,CJ8664/servo,mt2d2/servo,boghison/servo,walac/servo,upsuper/servo,SimonSapin/servo,CJ8664/servo,brendandahl/servo,mdibaiee/servo,fiji-flo/servo,zhangjunlei26/servo,peterjoel/servo,youprofit/servo,mbrubeck/servo,evilpie/servo,pyecs/servo,rentongzhang/servo,dati91/servo,huonw/servo,dsandeephegde/servo,wpgallih/servo,mdibaiee/servo,canaltinova/servo,ConnorGBrewster/servo,anthgur/servo,eddyb/servo,eddyb/servo,splav/servo,avadacatavra/servo,aweinstock314/servo,walac/servo,runarberg/servo,KiChjang/servo,rixrix/servo,anthgur/servo,notriddle/servo,tafia/servo,codemac/servo,cbrewster/servo,mt2d2/servo,dagnir/servo,ConnorGBrewster/servo,jgraham/servo,meh/servo,fiji-flo/servo,jlegendary/servo,hyowon/servo,aweinstock314/servo,tschneidereit/servo,ryancanhelpyou/servo,thiagopnts/servo,dvberkel/servo,GyrosOfWar/servo,rixrix/servo,dsandeephegde/servo,saratang/servo,KiChjang/servo,emilio/servo,upsuper/servo,rixrix/servo,hyowon/servo,pyecs/servo,wpgallih/servo,tempbottle/servo,evilpie/servo,GreenRecycleBin/servo,dati91/servo,meh/servo,pgonda/servo,hyowon/servo,steveklabnik/servo,jimberlage/servo,rixrix/servo,sadmansk/servo,notriddle/servo,saneyuki/servo,splav/servo,CJ8664/servo,nick-thompson/servo,deokjinkim/servo,evilpie/servo,larsbergstrom/servo,AnthonyBroadCrawford/servo,KiChjang/servo,RenaudParis/servo,fiji-flo/servo,nerith/servo,youprofit/servo,ConnorGBrewster/servo,jdramani/servo,mdibaiee/servo,bjwbell/servo,brendandahl/servo,DominoTree/servo,dagnir/servo,DominoTree/servo,canaltinova/servo,bjwbell/servo,saratang/servo,emilio/servo,pyfisch/servo,SimonSapin/servo,pyfisch/servo,samfoo/servo,CJ8664/servo,walac/servo,notriddle/servo,j3parker/servo,peterjoel/servo,anthgur/servo,youprofit/servo,SimonSapin/servo,bjwbell/servo,tschneidereit/servo,jdramani/servo,AnthonyBroadCrawford/servo,splav/servo,canaltinova/servo,fiji-flo/servo,rixrix/servo,saneyuki/servo,szeged/servo,nnethercote/servo,GyrosOfWar/servo,paulrouget/servo,pyfisch/servo,ryancanhelpyou/servo,SimonSapin/servo,rentongzhang/servo,dati91/servo,szeged/servo,tafia/servo,tempbottle/servo,kindersung/servo,pgonda/servo,vks/servo,dati91/servo,boghison/servo,avadacatavra/servo,nrc/servo,SimonSapin/servo,emilio/servo,canaltinova/servo,dagnir/servo,jimberlage/servo,akosel/servo,mt2d2/servo,pgonda/servo,CJ8664/servo,tschneidereit/servo,ryancanhelpyou/servo,boghison/servo,larsbergstrom/servo,deokjinkim/servo,dhananjay92/servo,notriddle/servo,pyfisch/servo,deokjinkim/servo,zhangjunlei26/servo,meh/servo,CJ8664/servo,nnethercote/servo,jgraham/servo,paulrouget/servo,upsuper/servo,nnethercote/servo,jimberlage/servo,fiji-flo/servo,wartman4404/servo,aweinstock314/servo,rixrix/servo,dhananjay92/servo,caldwell/servo,GreenRecycleBin/servo,evilpie/servo,SimonSapin/servo,notriddle/servo,jimberlage/servo,huonw/servo,g-k/servo,wpgallih/servo,pyfisch/servo,paulrouget/servo,jgraham/servo,jgraham/servo,cbrewster/servo,walac/servo,zentner-kyle/servo,AnthonyBroadCrawford/servo,KiChjang/servo,s142857/servo,dati91/servo,samfoo/servo,rentongzhang/servo,zentner-kyle/servo,dhananjay92/servo,saratang/servo,s142857/servo,kindersung/servo,thiagopnts/servo,s142857/servo,jdramani/servo,g-k/servo,cbrewster/servo,szeged/servo,nerith/servo,brendandahl/servo,mattnenterprise/servo,runarberg/servo,tschneidereit/servo,DominoTree/servo,anthgur/servo,nerith/servo,j3parker/servo,sadmansk/servo,rentongzhang/servo,zhangjunlei26/servo,zentner-kyle/servo,peterjoel/servo,eddyb/servo,WriterOfAlicrow/servo,zentner-kyle/servo,pyfisch/servo,steveklabnik/servo,vks/servo,rnestler/servo,kindersung/servo,s142857/servo,kindersung/servo,brendandahl/servo,mdibaiee/servo,deokjinkim/servo,dagnir/servo,wpgallih/servo,saneyuki/servo,deokjinkim/servo,nnethercote/servo