If we called the widget layout for x widgets, but the layouts returned less
geometries than this, we silently ignored the left-over widgets. If the layouts
returned more geometries, we crashed.
Fix this by verifying that the number of widgets and the number of geometries
are equal. If they are different, we use the smaller of the two.
Signed-off-by: Uli Schlachter <psychon@znc.in>