window: Hide windows on destroy

I thought I could get away with just unrealizing the
window, but it turns out that gtk_window_hide() is the
place where we remove grabs when a modal dialog goes
away, so we ended up with stuck grabs.

gtk/gtkwindow.c

@@ -7498,6 +7498,7 @@ gtk_window_destroy (GtkWindow *window)
         g_object_unref (item);
     }
 
+  gtk_window_hide (GTK_WIDGET (window));
   gtk_widget_unrealize (GTK_WIDGET (window));
 
   g_object_unref (window);