Fix --focus yet again.
Fix --focus yet again.

Zooming into the image must only be allowed if the adjusted
trimbox is larger than the input file. Basically this means that
we never zoom in after zooming out and that sounds reasonable.

Issue noticed and reported by Marc Espie, thanks again!

Signed-off-by: Tobias Stoeckmann <059b8b880f8441509ec8a65b50b4c6ae74ebea76@stoeckmann.org>

stoeckmann/xwallpaper,stoeckmann/xwallpaper