Fix wireframe without compositor.

Bug: 11995

In wireframeDrawXlib(), there was a check to not redraw the wireframe
if it had the same size as the previously drawn wireframe. This check is
also in wireframeDrawCairo(), but in the Xlib case it prevents correct
updates of the wireframe when cycling through identically sized windows.

Signed-off-by: Guus Sliepen <guus@debian.org>