message_list_view: Add a workaround for Chrome scrolling down bug.
message_list_view: Add a workaround for Chrome scrolling down bug.

Based on extensive manual testing with print-debugg (the exact
situation here was highly reproducible), in the absence of this line
here or slightly above here, Chrome 64 will consistently trigger an
extra scroll-forward-by-12000-pixels size downward scrolling event
immediately after it finishes rendering the 5th batch of ~100 messages
one gets from hitting the End key in `near:1` narrows.

I don't understand clearly why this change would protect against such
a Chrome bug, but my best guess is that Chrome was doing some sort of
incorrect optimization, and querying the scrollTop was forcing it to
come to a clear conclusion about the scrolling position before
appending more content.

But runs with the scrollTop() line not present in that function show a
scrollTop of around 25K in `append()` just before the call to
`render()`, and 37K at the end; while runs with this scrollTop line
always show 25K both before and after, so it does seem to work.

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