Before this fix, the code would restrict the pointer to be above
either the 1/2 mark or 2/3 mark of the page, depending on your
scrolling direction. This fix makes it so that the system leaves
your scroll and pointer alone when between the 1/5 mark and 4/5
mark. This means the user can read more messages on the screen
at a time before getting paginated.
(imported from commit 98f6319bf63181dd331e037ac20a0c15518725ea)