Commit 1ea22a52 broke the window reposition animation when it based the ::size-changed signal on the layout manager's bounding box instead of the MetaWindow::size-changed signal.
That happening because of the combination of:
- we adjust to window size changes immediately without animations
- closing a window triggers a change to a 0x0 bounding box which is not treated as a size change
Fix this by addressing the 2nd factor, and don't treat a change to a 0x0 bounding box as size change.
Fixes #2901 (closed)