top: tweak scroll coordinates msg handling (again)

top: tweak scroll coordinates msg handling (again)

An earlier commit improved the scroll coordinates
message performance by offloading most of the work
to those occasions when column headers were rebuilt.

The only remaining per-frame costs were the addition
of some terminfo escapes and the Frame_maxtask count.

This commit further reduces those per-frame costs to
the absolute minimum.

Reference:
commit fbfaa868babb0974c799d45e208619412afbdfef

Signed-off-by: Jim Warner <james.warner@comcast.net>