wayland: fix frame_redraw callback.

wayland: fix frame_redraw callback.

The redraw callback needs to be attached to the surface prior to the
commit. Otherwise, the callback notifies the next surface repaint,
which is not the desired behaviour. i.e. we want to be notified for
the surface we have just filled.

Another isse was the redraw_pending was reset before the actual completion
of the frame redraw callback function, thus causing concurrency issues.
e.g. the callback could have been called again, but with a NULL buffer.