GUI: Always try to show as many entries as possible in ListWidget.

In case there were less items in the list than on a page, it was possible
that a "scrollTo" call scrolled items out of the view even though all could
be displayed. This caused odd behavior in the load dialog in T7G. There
the list contains 10 entries. In case the last one was loaded via the dialog,
the next time it was brought up again it showed the 9th entry at the top
of the view and effectively hiding all the others. It furthermore did not
show the scroll bar because all entries would have fit onto one page.

To prevent this odd behavior, a boundary check has been added to all places
where the scroll position is set. This has been taken from "scrollToCurrent"
which already tried to prevent this.

This fixes the second issue described in bug #3610960
"T7G - savegame glitches".