xdg: try to handle missing set_window_geometry with Qt apps

xdg: try to handle missing set_window_geometry with Qt apps

Qt applications occasionally fail to call set_window_geometry after a
configure request, but do correctly update the actual surface extent.
This results in a mismatch between the window decorations (which follow
the logical geometry) and the visual size of the client area. As a
workaround, try to detect this case and ignore the out-of-date window
geometry.

Fixes: #1194