top: plug a minor hole in the vertical scrolling logic

top: plug a minor hole in the vertical scrolling logic

In that commit referenced below, a few edge cases were
addressed regarding vertical positioning involving any
'hidden' tasks. But, 2 additional edge cases remained.

In a running top, if the user employed 'other filters'
(o/O) or 'user filters' (u/U) proper vertical position
was not ensured. And, while this could be easily fixed
by striking the home/end or up/down arrow keys, it was
very poor etiquette to shift this burden to the users.

So, this patch plugs that gap, automating the process.

Reference(s):
commit c6e68e2fedc21b2537066433d1b50a60e06774eb

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