Collapsed mode is not so collapsed anymore

With b265e35f, now it's possible to resize the collapse window height, leading to this:

It's no big deal, next time xfce4-appfinder -c is launched or going to expanded and back to collapsed mode will properly resize the window, IMO it's better than breaking the app when scale > 1, see #49 (closed) for more details.

I created this issue as a reminder to check if there is anything that can be done (without geometry hints).