Fix serving files uploaded to S3.
Fix serving files uploaded to S3.

This was broken by the refactoring to realm_id_str in:
a261a6bbacf137cfbf70904e4a949bbc3e099c8c.

aakash-cr7/zulip,timabbott/zulip,AZtheAsian/zulip,calvinleenyc/zulip,KingxBanana/zulip,SmartPeople/zulip,eeshangarg/zulip,AZtheAsian/zulip,jphilipsen05/zulip,hackerkid/zulip,susansls/zulip,AZtheAsian/zulip,brockwhittaker/zulip,andersk/zulip,mahim97/zulip,vabs22/zulip,KingxBanana/zulip,Jianchun1/zulip,souravbadami/zulip,brainwane/zulip,amanharitsh123/zulip,Diptanshu8/zulip,j831/zulip,christi3k/zulip,SmartPeople/zulip,samatdav/zulip,calvinleenyc/zulip,zacps/zulip,umkay/zulip,shubhamdhama/zulip,jphilipsen05/zulip,ryanbackman/zulip,KingxBanana/zulip,aakash-cr7/zulip,jainayush975/zulip,rht/zulip,vaidap/zulip,shubhamdhama/zulip,kou/zulip,cosmicAsymmetry/zulip,kou/zulip,rht/zulip,AZtheAsian/zulip,jphilipsen05/zulip,joyhchen/zulip,mohsenSy/zulip,ahmadassaf/zulip,KingxBanana/zulip,tommyip/zulip,dhcrzf/zulip,verma-varsha/zulip,Diptanshu8/zulip,Juanvulcano/zulip,Galexrt/zulip,peguin40/zulip,showell/zulip,jphilipsen05/zulip,dawran6/zulip,shubhamdhama/zulip,dattatreya303/zulip,ahmadassaf/zulip,JPJPJPOPOP/zulip,zulip/zulip,verma-varsha/zulip,ahmadassaf/zulip,umkay/zulip,Galexrt/zulip,dhcrzf/zulip,eeshangarg/zulip,Juanvulcano/zulip,isht3/zulip,arpith/zulip,shubhamdhama/zulip,umkay/zulip,timabbott/zulip,amyliu345/zulip,amyliu345/zulip,mohsenSy/zulip,vaidap/zulip,dattatreya303/zulip,arpith/zulip,Juanvulcano/zulip,niftynei/zulip,rishig/zulip,susansls/zulip,brockwhittaker/zulip,andersk/zulip,kou/zulip,dawran6/zulip,eeshangarg/zulip,vabs22/zulip,krtkmj/zulip,paxapy/zulip,ryanbackman/zulip,niftynei/zulip,grave-w-grave/zulip,reyha/zulip,zulip/zulip,vaidap/zulip,cosmicAsymmetry/zulip,jainayush975/zulip,zacps/zulip,souravbadami/zulip,sup95/zulip,synicalsyntax/zulip,j831/zulip,j831/zulip,Galexrt/zulip,tommyip/zulip,TigorC/zulip,Jianchun1/zulip,amyliu345/zulip,niftynei/zulip,TigorC/zulip,Jianchun1/zulip,vikas-parashar/zulip,tommyip/zulip,tommyip/zulip,hackerkid/zulip,showell/zulip,jrowan/zulip,susansls/zulip,punchagan/zulip,punchagan/zulip,brockwhittaker/zulip,vabs22/zulip,amanharitsh123/zulip,souravbadami/zulip,paxapy/zulip,ahmadassaf/zulip,dhcrzf/zulip,souravbadami/zulip,SmartPeople/zulip,vaidap/zulip,arpith/zulip,susansls/zulip,amyliu345/zulip,rishig/zulip,sup95/zulip,reyha/zulip,sonali0901/zulip,peguin40/zulip,rishig/zulip,paxapy/zulip,paxapy/zulip,Jianchun1/zulip,amanharitsh123/zulip,paxapy/zulip,dawran6/zulip,blaze225/zulip,christi3k/zulip,rht/zulip,sonali0901/zulip,jackrzhang/zulip,ryanbackman/zulip,peguin40/zulip,aakash-cr7/zulip,hackerkid/zulip,mahim97/zulip,samatdav/zulip,hackerkid/zulip,PhilSk/zulip,andersk/zulip,blaze225/zulip,jrowan/zulip,verma-varsha/zulip,samatdav/zulip,synicalsyntax/zulip,kou/zulip,Galexrt/zulip,souravbadami/zulip,calvinleenyc/zulip,samatdav/zulip,peguin40/zulip,punchagan/zulip,brainwane/zulip,eeshangarg/zulip,Galexrt/zulip,calvinleenyc/zulip,brainwane/zulip,grave-w-grave/zulip,timabbott/zulip,grave-w-grave/zulip,KingxBanana/zulip,brainwane/zulip,cosmicAsymmetry/zulip,cosmicAsymmetry/zulip,Galexrt/zulip,andersk/zulip,zulip/zulip,brainwane/zulip,jainayush975/zulip,rht/zulip,jphilipsen05/zulip,krtkmj/zulip,sharmaeklavya2/zulip,joyhchen/zulip,zulip/zulip,Diptanshu8/zulip,punchagan/zulip,blaze225/zulip,shubhamdhama/zulip,tommyip/zulip,jainayush975/zulip,sup95/zulip,timabbott/zulip,SmartPeople/zulip,amyliu345/zulip,jrowan/zulip,joyhchen/zulip,sharmaeklavya2/zulip,timabbott/zulip,sonali0901/zulip,showell/zulip,grave-w-grave/zulip,dattatreya303/zulip,susansls/zulip,christi3k/zulip,aakash-cr7/zulip,brainwane/zulip,ryanbackman/zulip,umkay/zulip,j831/zulip,ahmadassaf/zulip,SmartPeople/zulip,vikas-parashar/zulip,mahim97/zulip,showell/zulip,rht/zulip,niftynei/zulip,arpith/zulip,sup95/zulip,TigorC/zulip,zacps/zulip,brockwhittaker/zulip,synicalsyntax/zulip,Diptanshu8/zulip,rishig/zulip,mahim97/zulip,isht3/zulip,rht/zulip,Juanvulcano/zulip,dhcrzf/zulip,sonali0901/zulip,sharmaeklavya2/zulip,jainayush975/zulip,reyha/zulip,JPJPJPOPOP/zulip,hackerkid/zulip,amanharitsh123/zulip,Juanvulcano/zulip,vabs22/zulip,vikas-parashar/zulip,ryanbackman/zulip,JPJPJPOPOP/zulip,sharmaeklavya2/zulip,rishig/zulip,peguin40/zulip,kou/zulip,andersk/zulip,showell/zulip,Jianchun1/zulip,dawran6/zulip,timabbott/zulip,vikas-parashar/zulip,krtkmj/zulip,hackerkid/zulip,dhcrzf/zulip,sup95/zulip,AZtheAsian/zulip,brainwane/zulip,jainayush975/zulip,krtkmj/zulip,mohsenSy/zulip,dhcrzf/zulip,andersk/zulip,JPJPJPOPOP/zulip,calvinleenyc/zulip,verma-varsha/zulip,reyha/zulip,PhilSk/zulip,rishig/zulip,grave-w-grave/zulip,vaidap/zulip,arpith/zulip,umkay/zulip,PhilSk/zulip,dhcrzf/zulip,arpith/zulip,mahim97/zulip,verma-varsha/zulip,PhilSk/zulip,samatdav/zulip,JPJPJPOPOP/zulip,blaze225/zulip,vabs22/zulip,samatdav/zulip,sonali0901/zulip,joyhchen/zulip,j831/zulip,shubhamdhama/zulip,amanharitsh123/zulip,KingxBanana/zulip,synicalsyntax/zulip,aakash-cr7/zulip,blaze225/zulip,rht/zulip,mohsenSy/zulip,isht3/zulip,ryanbackman/zulip,jackrzhang/zulip,krtkmj/zulip,tommyip/zulip,punchagan/zulip,jrowan/zulip,zulip/zulip,dattatreya303/zulip,grave-w-grave/zulip,dawran6/zulip,punchagan/zulip,jackrzhang/zulip,mahim97/zulip,sharmaeklavya2/zulip,susansls/zulip,zacps/zulip,cosmicAsymmetry/zulip,SmartPeople/zulip,eeshangarg/zulip,Jianchun1/zulip,shubhamdhama/zulip,andersk/zulip,zacps/zulip,synicalsyntax/zulip,reyha/zulip,PhilSk/zulip,paxapy/zulip,jackrzhang/zulip,vikas-parashar/zulip,niftynei/zulip,AZtheAsian/zulip,zulip/zulip,isht3/zulip,aakash-cr7/zulip,dawran6/zulip,mohsenSy/zulip,brockwhittaker/zulip,showell/zulip,Juanvulcano/zulip,umkay/zulip,TigorC/zulip,Diptanshu8/zulip,hackerkid/zulip,synicalsyntax/zulip,isht3/zulip,jackrzhang/zulip,timabbott/zulip,krtkmj/zulip,joyhchen/zulip,amyliu345/zulip,jackrzhang/zulip,kou/zulip,joyhchen/zulip,souravbadami/zulip,krtkmj/zulip,reyha/zulip,dattatreya303/zulip,Galexrt/zulip,vikas-parashar/zulip,umkay/zulip,TigorC/zulip,ahmadassaf/zulip,calvinleenyc/zulip,ahmadassaf/zulip,niftynei/zulip,synicalsyntax/zulip,TigorC/zulip,showell/zulip,christi3k/zulip,cosmicAsymmetry/zulip,verma-varsha/zulip,zacps/zulip,jrowan/zulip,mohsenSy/zulip,j831/zulip,christi3k/zulip,jrowan/zulip,sup95/zulip,zulip/zulip,amanharitsh123/zulip,JPJPJPOPOP/zulip,christi3k/zulip,brockwhittaker/zulip,jphilipsen05/zulip,peguin40/zulip,sonali0901/zulip,vabs22/zulip,eeshangarg/zulip,dattatreya303/zulip,PhilSk/zulip,sharmaeklavya2/zulip,blaze225/zulip,vaidap/zulip,jackrzhang/zulip,isht3/zulip,kou/zulip,punchagan/zulip,Diptanshu8/zulip,tommyip/zulip,rishig/zulip,eeshangarg/zulip