Fix missing 'current_url' value in registration flow.
Fix missing 'current_url' value in registration flow.

This fixes some tracebacks I got while testing the Zulip htpasswd SSO
functionality.

I think that this stopped working as a result of the Jinja2 migration.

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