window: unbind egl surface and context on surface release
window: unbind egl surface and context on surface release

Binding null read and write surfaces to an egl context is not standard

Reviewed-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

kwm81/weston,Fantu/compositor-spice,jonnylamb/weston,udoprog/weston,kwm81/weston,Gnurou/weston,jonnylamb/weston,Fantu/compositor-spice,sir-murray/weston,Tarnyko/weston-xdg_surface_present,mchalupa/weston,Tarnyko/weston-xdg_surface_present,giucam/weston,krezovic/weston,eyolfson/weston,eyolfson/weston,sir-murray/weston,krezovic/weston,giucam/weston,Fantu/compositor-spice,mchalupa/weston,Gnurou/weston,xorgy/weston,udoprog/weston,xorgy/weston