gdk_window_get_parent assertion failed sometimes.

[James Su <suzhe turbolinux com cn>]

I had reported this issue on bugzilla, the id is 115432.

When I close some kinds of window, gtk will go into a dead loop and report
the following error again and again:

(gtk-demo:30093): Gdk-CRITICAL **: file gdkwindow.c: line 526
(gdk_window_get_parent): assertion `GDK_IS_WINDOW (window)' failed

You may try to run gtk-demo, open Text Widget, then close the Text Widget
window, this error will be occurred.

This problem is appeared in gtk+2.2.2.