popovers: Fix actions popover menu positioning.
popovers: Fix actions popover menu positioning.

The main issue is that it wasn't doing the correct comparison; the old
logic that subtracted the viewport.scrollTop() was incorrect for how
our popovers seem to work.

Partially fixes #3741.

timabbott/zulip,susansls/zulip,verma-varsha/zulip,shubhamdhama/zulip,verma-varsha/zulip,tommyip/zulip,Galexrt/zulip,j831/zulip,brockwhittaker/zulip,jphilipsen05/zulip,mahim97/zulip,rishig/zulip,synicalsyntax/zulip,punchagan/zulip,kou/zulip,shubhamdhama/zulip,brockwhittaker/zulip,susansls/zulip,rht/zulip,timabbott/zulip,jrowan/zulip,showell/zulip,tommyip/zulip,showell/zulip,andersk/zulip,hackerkid/zulip,jackrzhang/zulip,PhilSk/zulip,vabs22/zulip,punchagan/zulip,kou/zulip,eeshangarg/zulip,brockwhittaker/zulip,tommyip/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,ryanbackman/zulip,eeshangarg/zulip,souravbadami/zulip,jainayush975/zulip,zulip/zulip,christi3k/zulip,andersk/zulip,vaidap/zulip,synicalsyntax/zulip,verma-varsha/zulip,ryanbackman/zulip,andersk/zulip,zulip/zulip,christi3k/zulip,Galexrt/zulip,showell/zulip,dhcrzf/zulip,susansls/zulip,Galexrt/zulip,jphilipsen05/zulip,vaidap/zulip,mahim97/zulip,vaidap/zulip,aakash-cr7/zulip,showell/zulip,dhcrzf/zulip,punchagan/zulip,vabs22/zulip,synicalsyntax/zulip,j831/zulip,ryanbackman/zulip,jainayush975/zulip,brainwane/zulip,brainwane/zulip,zulip/zulip,hackerkid/zulip,rishig/zulip,timabbott/zulip,kou/zulip,brockwhittaker/zulip,jrowan/zulip,SmartPeople/zulip,rishig/zulip,hackerkid/zulip,showell/zulip,jackrzhang/zulip,brockwhittaker/zulip,jackrzhang/zulip,rishig/zulip,ryanbackman/zulip,tommyip/zulip,zulip/zulip,tommyip/zulip,SmartPeople/zulip,ryanbackman/zulip,JPJPJPOPOP/zulip,Galexrt/zulip,brockwhittaker/zulip,SmartPeople/zulip,synicalsyntax/zulip,rht/zulip,verma-varsha/zulip,jainayush975/zulip,rht/zulip,amanharitsh123/zulip,christi3k/zulip,aakash-cr7/zulip,shubhamdhama/zulip,jackrzhang/zulip,mahim97/zulip,hackerkid/zulip,mahim97/zulip,timabbott/zulip,kou/zulip,SmartPeople/zulip,aakash-cr7/zulip,shubhamdhama/zulip,brainwane/zulip,PhilSk/zulip,jrowan/zulip,zulip/zulip,susansls/zulip,dhcrzf/zulip,timabbott/zulip,punchagan/zulip,mahim97/zulip,souravbadami/zulip,amanharitsh123/zulip,jrowan/zulip,vaidap/zulip,souravbadami/zulip,timabbott/zulip,jackrzhang/zulip,rht/zulip,jainayush975/zulip,vaidap/zulip,shubhamdhama/zulip,andersk/zulip,amanharitsh123/zulip,andersk/zulip,jrowan/zulip,souravbadami/zulip,PhilSk/zulip,vabs22/zulip,showell/zulip,tommyip/zulip,dawran6/zulip,souravbadami/zulip,ryanbackman/zulip,Galexrt/zulip,rishig/zulip,jphilipsen05/zulip,hackerkid/zulip,timabbott/zulip,showell/zulip,SmartPeople/zulip,amanharitsh123/zulip,christi3k/zulip,hackerkid/zulip,mahim97/zulip,kou/zulip,rishig/zulip,shubhamdhama/zulip,dawran6/zulip,christi3k/zulip,jackrzhang/zulip,jackrzhang/zulip,susansls/zulip,punchagan/zulip,dhcrzf/zulip,synicalsyntax/zulip,rht/zulip,aakash-cr7/zulip,vaidap/zulip,zulip/zulip,aakash-cr7/zulip,dawran6/zulip,rishig/zulip,vabs22/zulip,PhilSk/zulip,dawran6/zulip,dawran6/zulip,zulip/zulip,eeshangarg/zulip,vabs22/zulip,PhilSk/zulip,rht/zulip,JPJPJPOPOP/zulip,vabs22/zulip,dhcrzf/zulip,dawran6/zulip,eeshangarg/zulip,Galexrt/zulip,synicalsyntax/zulip,JPJPJPOPOP/zulip,andersk/zulip,kou/zulip,j831/zulip,jphilipsen05/zulip,brainwane/zulip,souravbadami/zulip,hackerkid/zulip,punchagan/zulip,brainwane/zulip,JPJPJPOPOP/zulip,kou/zulip,PhilSk/zulip,verma-varsha/zulip,j831/zulip,Galexrt/zulip,christi3k/zulip,aakash-cr7/zulip,dhcrzf/zulip,j831/zulip,amanharitsh123/zulip,jainayush975/zulip,jrowan/zulip,punchagan/zulip,synicalsyntax/zulip,brainwane/zulip,susansls/zulip,SmartPeople/zulip,tommyip/zulip,verma-varsha/zulip,jainayush975/zulip,andersk/zulip,JPJPJPOPOP/zulip,j831/zulip,jphilipsen05/zulip,shubhamdhama/zulip,amanharitsh123/zulip,brainwane/zulip,JPJPJPOPOP/zulip,jphilipsen05/zulip,eeshangarg/zulip,dhcrzf/zulip