compositor: Dont set the opaque region if we have an overall surface alpha
compositor: Dont set the opaque region if we have an overall surface alpha

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