After 20176d03, the Wayland backend only synchronizes with the compositor after a geometry was set, and it was different from the current geometry.
That commit was mistakenly comparing the geometry before chaining up, which would yield a false negative on the case where the client wouldn't call set_geometry() before commit().
Fix that by caching the old geometry locally, chain up (and thus apply the new geometry rectangle), then comparing the old and current geometry rectangles.
Fixes #150 (closed)
(This should be cherry-picked to gnome-3-28 too)