Improve error handling in is_current_user().
Improve error handling in is_current_user().

Realm bots have a owner of `null` but that is not explicity handled
in `is_current_user()`.

ryanbackman/zulip,aakash-cr7/zulip,KingxBanana/zulip,timabbott/zulip,arpith/zulip,arpith/zulip,Juanvulcano/zulip,jainayush975/zulip,niftynei/zulip,Juanvulcano/zulip,timabbott/zulip,timabbott/zulip,christi3k/zulip,punchagan/zulip,susansls/zulip,joyhchen/zulip,shubhamdhama/zulip,brockwhittaker/zulip,jrowan/zulip,dhcrzf/zulip,amanharitsh123/zulip,Diptanshu8/zulip,eeshangarg/zulip,rishig/zulip,hackerkid/zulip,christi3k/zulip,niftynei/zulip,dhcrzf/zulip,dattatreya303/zulip,isht3/zulip,andersk/zulip,jackrzhang/zulip,kou/zulip,kou/zulip,hackerkid/zulip,vabs22/zulip,AZtheAsian/zulip,samatdav/zulip,amyliu345/zulip,KingxBanana/zulip,eeshangarg/zulip,timabbott/zulip,jainayush975/zulip,KingxBanana/zulip,tommyip/zulip,PhilSk/zulip,brockwhittaker/zulip,verma-varsha/zulip,showell/zulip,JPJPJPOPOP/zulip,christi3k/zulip,vabs22/zulip,AZtheAsian/zulip,synicalsyntax/zulip,susansls/zulip,jackrzhang/zulip,rht/zulip,AZtheAsian/zulip,jainayush975/zulip,cosmicAsymmetry/zulip,joyhchen/zulip,niftynei/zulip,SmartPeople/zulip,samatdav/zulip,brainwane/zulip,showell/zulip,vaidap/zulip,cosmicAsymmetry/zulip,mahim97/zulip,hackerkid/zulip,KingxBanana/zulip,dawran6/zulip,dhcrzf/zulip,jackrzhang/zulip,zulip/zulip,TigorC/zulip,jainayush975/zulip,vabs22/zulip,rishig/zulip,rht/zulip,sonali0901/zulip,Diptanshu8/zulip,cosmicAsymmetry/zulip,susansls/zulip,arpith/zulip,synicalsyntax/zulip,showell/zulip,Diptanshu8/zulip,brainwane/zulip,zacps/zulip,christi3k/zulip,verma-varsha/zulip,PhilSk/zulip,Diptanshu8/zulip,jackrzhang/zulip,brockwhittaker/zulip,dattatreya303/zulip,jphilipsen05/zulip,showell/zulip,amyliu345/zulip,rht/zulip,blaze225/zulip,hackerkid/zulip,brockwhittaker/zulip,j831/zulip,JPJPJPOPOP/zulip,dattatreya303/zulip,TigorC/zulip,hackerkid/zulip,JPJPJPOPOP/zulip,cosmicAsymmetry/zulip,punchagan/zulip,jainayush975/zulip,eeshangarg/zulip,synicalsyntax/zulip,ryanbackman/zulip,verma-varsha/zulip,timabbott/zulip,KingxBanana/zulip,blaze225/zulip,eeshangarg/zulip,punchagan/zulip,AZtheAsian/zulip,shubhamdhama/zulip,synicalsyntax/zulip,amyliu345/zulip,sonali0901/zulip,vabs22/zulip,rishig/zulip,Juanvulcano/zulip,vabs22/zulip,SmartPeople/zulip,rht/zulip,verma-varsha/zulip,Galexrt/zulip,blaze225/zulip,aakash-cr7/zulip,rht/zulip,TigorC/zulip,amanharitsh123/zulip,zacps/zulip,susansls/zulip,amyliu345/zulip,dhcrzf/zulip,j831/zulip,jrowan/zulip,brainwane/zulip,andersk/zulip,christi3k/zulip,andersk/zulip,JPJPJPOPOP/zulip,jrowan/zulip,synicalsyntax/zulip,samatdav/zulip,zulip/zulip,jrowan/zulip,hackerkid/zulip,SmartPeople/zulip,jainayush975/zulip,sharmaeklavya2/zulip,j831/zulip,souravbadami/zulip,rht/zulip,jackrzhang/zulip,sharmaeklavya2/zulip,vaidap/zulip,zacps/zulip,dhcrzf/zulip,dhcrzf/zulip,blaze225/zulip,brockwhittaker/zulip,tommyip/zulip,amanharitsh123/zulip,JPJPJPOPOP/zulip,shubhamdhama/zulip,TigorC/zulip,jphilipsen05/zulip,joyhchen/zulip,j831/zulip,tommyip/zulip,Galexrt/zulip,SmartPeople/zulip,shubhamdhama/zulip,andersk/zulip,SmartPeople/zulip,sharmaeklavya2/zulip,dawran6/zulip,PhilSk/zulip,dawran6/zulip,isht3/zulip,arpith/zulip,j831/zulip,zulip/zulip,vabs22/zulip,zulip/zulip,zulip/zulip,souravbadami/zulip,punchagan/zulip,Galexrt/zulip,ryanbackman/zulip,showell/zulip,amyliu345/zulip,vaidap/zulip,dawran6/zulip,joyhchen/zulip,samatdav/zulip,samatdav/zulip,souravbadami/zulip,brainwane/zulip,jphilipsen05/zulip,mahim97/zulip,mahim97/zulip,brockwhittaker/zulip,sonali0901/zulip,cosmicAsymmetry/zulip,synicalsyntax/zulip,Diptanshu8/zulip,JPJPJPOPOP/zulip,sonali0901/zulip,blaze225/zulip,punchagan/zulip,cosmicAsymmetry/zulip,dattatreya303/zulip,arpith/zulip,jrowan/zulip,brainwane/zulip,tommyip/zulip,aakash-cr7/zulip,souravbadami/zulip,isht3/zulip,jackrzhang/zulip,niftynei/zulip,joyhchen/zulip,susansls/zulip,PhilSk/zulip,mahim97/zulip,Juanvulcano/zulip,SmartPeople/zulip,susansls/zulip,amyliu345/zulip,souravbadami/zulip,zacps/zulip,timabbott/zulip,andersk/zulip,tommyip/zulip,rishig/zulip,Diptanshu8/zulip,timabbott/zulip,andersk/zulip,kou/zulip,mahim97/zulip,zulip/zulip,zacps/zulip,eeshangarg/zulip,kou/zulip,vaidap/zulip,amanharitsh123/zulip,shubhamdhama/zulip,brainwane/zulip,ryanbackman/zulip,isht3/zulip,niftynei/zulip,PhilSk/zulip,kou/zulip,jphilipsen05/zulip,amanharitsh123/zulip,punchagan/zulip,AZtheAsian/zulip,andersk/zulip,tommyip/zulip,sharmaeklavya2/zulip,zulip/zulip,vaidap/zulip,synicalsyntax/zulip,kou/zulip,tommyip/zulip,Juanvulcano/zulip,jphilipsen05/zulip,joyhchen/zulip,rht/zulip,j831/zulip,rishig/zulip,ryanbackman/zulip,showell/zulip,niftynei/zulip,kou/zulip,souravbadami/zulip,christi3k/zulip,shubhamdhama/zulip,Galexrt/zulip,isht3/zulip,AZtheAsian/zulip,dawran6/zulip,dhcrzf/zulip,ryanbackman/zulip,dattatreya303/zulip,dawran6/zulip,Galexrt/zulip,sonali0901/zulip,KingxBanana/zulip,rishig/zulip,Galexrt/zulip,dattatreya303/zulip,showell/zulip,hackerkid/zulip,brainwane/zulip,samatdav/zulip,TigorC/zulip,punchagan/zulip,sonali0901/zulip,jphilipsen05/zulip,vaidap/zulip,amanharitsh123/zulip,verma-varsha/zulip,jrowan/zulip,sharmaeklavya2/zulip,Juanvulcano/zulip,aakash-cr7/zulip,Galexrt/zulip,arpith/zulip,mahim97/zulip,TigorC/zulip,zacps/zulip,isht3/zulip,aakash-cr7/zulip,aakash-cr7/zulip,eeshangarg/zulip,sharmaeklavya2/zulip,jackrzhang/zulip,verma-varsha/zulip,rishig/zulip,eeshangarg/zulip,PhilSk/zulip,blaze225/zulip,shubhamdhama/zulip