panels: queue draw instead of commiting the surface

If we commit too early and GTK hasn't updated the buffer the compositor will terminate us due to the buffer size not matching the scale.

A draw will eventually commit the surface. This makes sure we don't commit without giving GTK a chance to update e.g. the buffer size.

This is not ideal as we invalidate the complete surface causing a full redraw.

Closes: #1050 Signed-off-by: Guido Günther agx@sigxcpu.org