Commit 91d8a32f25 let WindowClone forward the size-changed signal
of the "real" window, disconnecting the signal handler when the
clone is destroyed. In case the clone was destroyed due to the
MetaWindowActor being closed, this results in a warning
(gsignal.c:2392: instance `0x2a3fac0' has no handler with id `2955').
Handle the case where the original window is destroyed before its
clone.
00df20c618