message_edit: Fix exception closing "view source".
message_edit: Fix exception closing "view source".

This fixes a regression introduced in
81a575e4d509af68b0dcf8419212444e6c883d0d.

mahim97/zulip,tommyip/zulip,vabs22/zulip,brainwane/zulip,mahim97/zulip,christi3k/zulip,shubhamdhama/zulip,dhcrzf/zulip,zulip/zulip,andersk/zulip,shubhamdhama/zulip,jackrzhang/zulip,vaidap/zulip,Galexrt/zulip,vaidap/zulip,brainwane/zulip,ryanbackman/zulip,verma-varsha/zulip,christi3k/zulip,rht/zulip,brainwane/zulip,zulip/zulip,amanharitsh123/zulip,kou/zulip,hackerkid/zulip,jrowan/zulip,vabs22/zulip,jackrzhang/zulip,synicalsyntax/zulip,hackerkid/zulip,jphilipsen05/zulip,andersk/zulip,vaidap/zulip,ryanbackman/zulip,showell/zulip,amanharitsh123/zulip,rishig/zulip,kou/zulip,vaidap/zulip,showell/zulip,rishig/zulip,rht/zulip,tommyip/zulip,dhcrzf/zulip,mahim97/zulip,jrowan/zulip,rht/zulip,kou/zulip,jrowan/zulip,andersk/zulip,jackrzhang/zulip,j831/zulip,zulip/zulip,mahim97/zulip,kou/zulip,j831/zulip,brainwane/zulip,rishig/zulip,christi3k/zulip,brockwhittaker/zulip,punchagan/zulip,hackerkid/zulip,jphilipsen05/zulip,timabbott/zulip,tommyip/zulip,rishig/zulip,hackerkid/zulip,shubhamdhama/zulip,amanharitsh123/zulip,eeshangarg/zulip,jackrzhang/zulip,zulip/zulip,mahim97/zulip,vabs22/zulip,j831/zulip,synicalsyntax/zulip,rishig/zulip,Galexrt/zulip,dhcrzf/zulip,Galexrt/zulip,jphilipsen05/zulip,tommyip/zulip,showell/zulip,Galexrt/zulip,vabs22/zulip,punchagan/zulip,showell/zulip,jackrzhang/zulip,ryanbackman/zulip,synicalsyntax/zulip,j831/zulip,ryanbackman/zulip,jphilipsen05/zulip,vabs22/zulip,andersk/zulip,verma-varsha/zulip,verma-varsha/zulip,shubhamdhama/zulip,timabbott/zulip,tommyip/zulip,jrowan/zulip,tommyip/zulip,kou/zulip,verma-varsha/zulip,amanharitsh123/zulip,punchagan/zulip,hackerkid/zulip,j831/zulip,christi3k/zulip,vabs22/zulip,brainwane/zulip,andersk/zulip,timabbott/zulip,punchagan/zulip,jrowan/zulip,timabbott/zulip,rishig/zulip,showell/zulip,ryanbackman/zulip,andersk/zulip,punchagan/zulip,jphilipsen05/zulip,shubhamdhama/zulip,dhcrzf/zulip,punchagan/zulip,rishig/zulip,eeshangarg/zulip,vaidap/zulip,punchagan/zulip,amanharitsh123/zulip,jphilipsen05/zulip,rht/zulip,eeshangarg/zulip,timabbott/zulip,christi3k/zulip,brockwhittaker/zulip,ryanbackman/zulip,amanharitsh123/zulip,brainwane/zulip,hackerkid/zulip,brockwhittaker/zulip,shubhamdhama/zulip,rht/zulip,brainwane/zulip,j831/zulip,brockwhittaker/zulip,verma-varsha/zulip,dhcrzf/zulip,synicalsyntax/zulip,brockwhittaker/zulip,eeshangarg/zulip,jackrzhang/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,christi3k/zulip,mahim97/zulip,Galexrt/zulip,Galexrt/zulip,hackerkid/zulip,synicalsyntax/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,verma-varsha/zulip,synicalsyntax/zulip,dhcrzf/zulip,synicalsyntax/zulip,shubhamdhama/zulip,eeshangarg/zulip,jackrzhang/zulip,brockwhittaker/zulip,dhcrzf/zulip,timabbott/zulip,vaidap/zulip,kou/zulip,jrowan/zulip,tommyip/zulip,Galexrt/zulip,showell/zulip,andersk/zulip,showell/zulip,zulip/zulip,timabbott/zulip