Backport of "wayland/wlbuffer: just return if used_by_compositor is true when attach" into 1.16
Backport of !339 (merged) "wayland/wlbuffer: just return if used_by_compositor is true when attach".
Commits:
- 9d0ba0f2 wayland/wlbuffer: just return if used_by_compositor is true when attach