ui: Fix wrong usage of scrolling to top in ui.updateScrollbar.
ui: Fix wrong usage of scrolling to top in ui.updateScrollbar.

This was a bug introduced in 2363c9955aa2b69f7b5bcf5ef146b29607417d37.

Fixes: #11141.

kou/zulip,rht/zulip,hackerkid/zulip,kou/zulip,synicalsyntax/zulip,punchagan/zulip,dhcrzf/zulip,brainwane/zulip,dhcrzf/zulip,shubhamdhama/zulip,tommyip/zulip,synicalsyntax/zulip,zulip/zulip,tommyip/zulip,dhcrzf/zulip,eeshangarg/zulip,eeshangarg/zulip,rishig/zulip,showell/zulip,rishig/zulip,synicalsyntax/zulip,kou/zulip,rht/zulip,showell/zulip,rishig/zulip,showell/zulip,shubhamdhama/zulip,timabbott/zulip,zulip/zulip,hackerkid/zulip,rishig/zulip,synicalsyntax/zulip,shubhamdhama/zulip,synicalsyntax/zulip,timabbott/zulip,punchagan/zulip,kou/zulip,brainwane/zulip,timabbott/zulip,synicalsyntax/zulip,hackerkid/zulip,shubhamdhama/zulip,punchagan/zulip,showell/zulip,eeshangarg/zulip,zulip/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,showell/zulip,rht/zulip,brainwane/zulip,timabbott/zulip,hackerkid/zulip,dhcrzf/zulip,eeshangarg/zulip,synicalsyntax/zulip,rht/zulip,tommyip/zulip,zulip/zulip,punchagan/zulip,kou/zulip,brainwane/zulip,andersk/zulip,rht/zulip,zulip/zulip,punchagan/zulip,tommyip/zulip,tommyip/zulip,brainwane/zulip,punchagan/zulip,eeshangarg/zulip,showell/zulip,rishig/zulip,eeshangarg/zulip,brainwane/zulip,dhcrzf/zulip,tommyip/zulip,andersk/zulip,tommyip/zulip,rht/zulip,timabbott/zulip,shubhamdhama/zulip,dhcrzf/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,timabbott/zulip,shubhamdhama/zulip,andersk/zulip,rishig/zulip,shubhamdhama/zulip,hackerkid/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,andersk/zulip,brainwane/zulip,timabbott/zulip,punchagan/zulip,andersk/zulip,showell/zulip,rishig/zulip,kou/zulip,dhcrzf/zulip