auto merge of #15719 : michaelwoerister/rust/global_var_null_span_fix, r=alexcrichton
auto merge of #15719 : michaelwoerister/rust/global_var_null_span_fix, r=alexcrichton

This should fix issue #15541. It would be good to have an test case for this would also be nice but I haven't had the time to write one. The change is very small though and it doesn't break anything in the existing test suite, so I guess we can add it without test for now.

mahkoh/rust,GBGamer/rust,nham/rust,carols10cents/rust,ktossell/rust,jbclements/rust,robertg/rust,P1start/rust,erickt/rust,nwin/rust,rprichard/rust,mahkoh/rust,P1start/rust,jashank/rust,kimroen/rust,pelmers/rust,graydon/rust,reem/rust,jbclements/rust,jashank/rust,mihneadb/rust,aepsil0n/rust,jroesch/rust,richo/rust,andars/rust,quornian/rust,philyoon/rust,zubron/rust,vhbit/rust,jroesch/rust,omasanori/rust,ktossell/rust,quornian/rust,kimroen/rust,carols10cents/rust,mahkoh/rust,seanrivera/rust,sae-bom/rust,mdinger/rust,TheNeikos/rust,bombless/rust,ebfull/rust,quornian/rust,miniupnp/rust,seanrivera/rust,pshc/rust,AerialX/rust,GBGamer/rust,aneeshusa/rust,cllns/rust,graydon/rust,philyoon/rust,jbclements/rust,ejjeong/rust,philyoon/rust,kwantam/rust,GBGamer/rust,zachwick/rust,miniupnp/rust,seanrivera/rust,aneeshusa/rust,jroesch/rust,defuz/rust,pshc/rust,reem/rust,kimroen/rust,rohitjoshi/rust,zaeleus/rust,victorvde/rust,untitaker/rust,ruud-v-a/rust,carols10cents/rust,jbclements/rust,andars/rust,vhbit/rust,rohitjoshi/rust,nwin/rust,untitaker/rust,zubron/rust,0x73/rust,untitaker/rust,zachwick/rust,ruud-v-a/rust,ruud-v-a/rust,AerialX/rust,erickt/rust,bombless/rust,zubron/rust,gifnksm/rust,jbclements/rust,nham/rust,aepsil0n/rust,AerialX/rust-rt-minimal,P1start/rust,aidancully/rust,P1start/rust,quornian/rust,dwillmer/rust,mvdnes/rust,mvdnes/rust,mihneadb/rust,erickt/rust,mihneadb/rust,nham/rust,jashank/rust,AerialX/rust-rt-minimal,reem/rust,jbclements/rust,krzysz00/rust,rprichard/rust,jbclements/rust,krzysz00/rust,mahkoh/rust,aidancully/rust,nham/rust,nwin/rust,ejjeong/rust,seanrivera/rust,nham/rust,kimroen/rust,vhbit/rust,cllns/rust,richo/rust,dinfuehr/rust,XMPPwocky/rust,ebfull/rust,robertg/rust,XMPPwocky/rust,philyoon/rust,barosl/rust,pczarn/rust,pczarn/rust,erickt/rust,gifnksm/rust,ejjeong/rust,TheNeikos/rust,hauleth/rust,kimroen/rust,mvdnes/rust,jroesch/rust,KokaKiwi/rust,aidancully/rust,P1start/rust,GBGamer/rust,pshc/rust,andars/rust,l0kod/rust,bombless/rust,miniupnp/rust,ruud-v-a/rust,zachwick/rust,robertg/rust,hauleth/rust,kwantam/rust,dinfuehr/rust,zachwick/rust,omasanori/rust,jroesch/rust,emk/rust,AerialX/rust-rt-minimal,graydon/rust,bombless/rust,emk/rust,rprichard/rust,rohitjoshi/rust,nwin/rust,XMPPwocky/rust,zubron/rust,nwin/rust,l0kod/rust,kwantam/rust,vhbit/rust,AerialX/rust-rt-minimal,aidancully/rust,bombless/rust,AerialX/rust-rt-minimal,mihneadb/rust,ejjeong/rust,mdinger/rust,dwillmer/rust,miniupnp/rust,0x73/rust,zachwick/rust,TheNeikos/rust,pelmers/rust,miniupnp/rust,zachwick/rust,mihneadb/rust,P1start/rust,barosl/rust,KokaKiwi/rust,avdi/rust,nwin/rust,jashank/rust,zubron/rust,GBGamer/rust,cllns/rust,rohitjoshi/rust,KokaKiwi/rust,ebfull/rust,robertg/rust,kwantam/rust,mdinger/rust,gifnksm/rust,pelmers/rust,nwin/rust,zaeleus/rust,dinfuehr/rust,untitaker/rust,richo/rust,nham/rust,kwantam/rust,l0kod/rust,hauleth/rust,vhbit/rust,aneeshusa/rust,philyoon/rust,pelmers/rust,reem/rust,XMPPwocky/rust,barosl/rust,dwillmer/rust,l0kod/rust,krzysz00/rust,jashank/rust,0x73/rust,omasanori/rust,GBGamer/rust,ktossell/rust,miniupnp/rust,krzysz00/rust,graydon/rust,KokaKiwi/rust,jashank/rust,aneeshusa/rust,defuz/rust,kwantam/rust,dwillmer/rust,erickt/rust,sae-bom/rust,0x73/rust,sae-bom/rust,carols10cents/rust,mdinger/rust,dwillmer/rust,rprichard/rust,defuz/rust,pczarn/rust,ebfull/rust,pelmers/rust,aidancully/rust,aneeshusa/rust,pczarn/rust,aepsil0n/rust,mahkoh/rust,reem/rust,nwin/rust,AerialX/rust,l0kod/rust,avdi/rust,pczarn/rust,omasanori/rust,l0kod/rust,andars/rust,vhbit/rust,rprichard/rust,rohitjoshi/rust,sae-bom/rust,0x73/rust,sae-bom/rust,dinfuehr/rust,andars/rust,graydon/rust,pshc/rust,richo/rust,omasanori/rust,pczarn/rust,aneeshusa/rust,zubron/rust,GBGamer/rust,dinfuehr/rust,emk/rust,cllns/rust,kimroen/rust,quornian/rust,krzysz00/rust,carols10cents/rust,dwillmer/rust,bombless/rust,richo/rust,erickt/rust,avdi/rust,victorvde/rust,pshc/rust,aepsil0n/rust,GBGamer/rust,zaeleus/rust,ktossell/rust,pczarn/rust,emk/rust,victorvde/rust,l0kod/rust,seanrivera/rust,nham/rust,pshc/rust,emk/rust,0x73/rust,jbclements/rust,dwillmer/rust,carols10cents/rust,XMPPwocky/rust,pelmers/rust,KokaKiwi/rust,P1start/rust,TheNeikos/rust,kimroen/rust,mihneadb/rust,robertg/rust,mvdnes/rust,rprichard/rust,defuz/rust,emk/rust,cllns/rust,ruud-v-a/rust,untitaker/rust,aepsil0n/rust,barosl/rust,reem/rust,mahkoh/rust,ejjeong/rust,victorvde/rust,zaeleus/rust,miniupnp/rust,KokaKiwi/rust,zaeleus/rust,philyoon/rust,dinfuehr/rust,ebfull/rust,jashank/rust,hauleth/rust,jashank/rust,sae-bom/rust,ejjeong/rust,barosl/rust,victorvde/rust,defuz/rust,zaeleus/rust,gifnksm/rust,quornian/rust,avdi/rust,gifnksm/rust,omasanori/rust,XMPPwocky/rust,zubron/rust,AerialX/rust,hauleth/rust,vhbit/rust,untitaker/rust,aidancully/rust,ktossell/rust,barosl/rust,jroesch/rust,robertg/rust,seanrivera/rust,richo/rust,hauleth/rust,erickt/rust,avdi/rust,ebfull/rust,jroesch/rust,dwillmer/rust,aepsil0n/rust,mdinger/rust,ktossell/rust,quornian/rust,TheNeikos/rust,zubron/rust,graydon/rust,pshc/ru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