[window] Fix removing children from a window
[window] Fix removing children from a window

If you tried to remove a child from a window it would segfault in the
dispose. Copy the same logic that MxBin uses.

clutter-project/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,pwithnall/mx,pwithnall/mx,jonnylamb/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx