compositor: check viewport source rect validity

compositor: check viewport source rect validity

wp_viewporter spec requires protocol errors when the viewport is outside
the buffer area.

The viewport is checked in wl_surface.commit handler as the error needs
to be delivered as a reply to the commit, not at state apply time later
(e.g. with synchronized sub-surfaces, or at render time).

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>