Fix pane position bug

Argh. Maxint is not at the bottom or at the right. We have to check
against the size of the window to determine we are not saving a maximized
position.  Here is a fix.

Signed-off-by: Robert C. Helling <helling@atdotde.de>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>