[X11] Fix client resize on moving
This is aimed at fixing issue #1674 (closed) on X11 (the Wayland part was addressed with commit 0e97c055 and !1784 (merged) already).
On X11:
- mutter prevents the client from resizing even when moving
- When mutter prevents the client from resizing it uses the wrong size so the client shrunks rapidly
Closes: #1674 (closed)
Edited by Olivier Fourdan