[xwayland regression] Commit fa7b1c20 breaks Xwayland rootful with libdecor

Commit fa7b1c20 breaks Xwayland rootful with libdecor by adding a test for size_chnaged that wasn't there before.

What happens that is that, on xrandr change, the root window size changes, the config notify is triggered, but the root size is already chnaged, so it doesn;t chnage the libedecor size causing a discrepancy between what libdecor "thinks" and the actual size.

Them on next focus change, the size is reverted to the size from libdecor.