This fixes a case that was overlooked in !1036 (merged) - when we have a geometry scale > 1 and Wayland subsurfaces that have an offset to their parent surface (which is often the case when the toplevel surface includes decoration/shadows etc.), we have to add extra offset to their opaque regions so they match their 'visible' location.
This is necessary as
meta_cullable_cull_out_children moves the coordinate
system during culling, but does not know about geometry scale.
Also, remove the redundant check for
window_actor - we only hit this code
path if a
window_actor culls out its children.
Fixes #1095 (closed)
Tested this with the gstreamer wayland demo, see !148 (merged), and Firefox