[gtk+] tooltip: Fix warning with GtkCellRendererAccel

[Matthias Clasen <matthiasc src gnome org>]

commit c849b8edd664b7e84b42a61e95dad9f8e0b287f7
Author: Bastien Nocera <hadess hadess net>
Date:   Fri Sep 5 15:22:47 2014 +0200

    tooltip: Fix warning with GtkCellRendererAccel
    
    (gnome-shell-extension-prefs:22382): GLib-GObject-WARNING **: invalid cast from 'GtkInvisible' to 
'GtkWindow'
    (gnome-shell-extension-prefs:22382): Gtk-CRITICAL **: gtk_window_set_transient_for: assertion 'parent == 
NULL || GTK_IS_WINDOW (parent)' failed
    
     #1  0x00007fffeeb81a12 in g_log (log_domain=log_domain entry=0x7fffeeea3464 "GLib-GObject", 
log_level=log_level entry=G_LOG_LEVEL_WARNING, format=format entry=0x7fffeeeaa878 "invalid cast from '%s' to 
'%s'") at gmessages.c:1079
     #2  0x00007fffeee9c2a9 in g_type_check_instance_cast (type_instance=0xb314c0, iface_type=iface_type 
entry=9020048) at gtype.c:4021
     #3  0x00007ffff0a06e25 in gtk_tooltip_set_last_window (tooltip=tooltip entry=0xbb8c10, window=<optimized 
out>) at gtktooltip.c:910
     #4  0x00007ffff0a08dfd in _gtk_tooltip_handle_event (event=event entry=0xbf72c0) at gtktooltip.c:1538
     #5  0x00007ffff090d7a9 in gtk_main_do_event (event=0xbf72c0) at gtkmain.c:1785
     #6  0x00007ffff0496ab2 in gdk_event_source_dispatch (source=<optimized out>, callback=<optimized out>, 
user_data=<optimized out>) at gdkeventsource.c:364
     #7  0x00007fffeeb7a8c3 in g_main_dispatch (context=0x807300) at gmain.c:3067
    
    https://bugzilla.gnome.org/show_bug.cgi?id=736131

 gtk/gtktooltip.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtktooltip.c b/gtk/gtktooltip.c
index f7a6ab9..3e585e3 100644
--- a/gtk/gtktooltip.c
+++ b/gtk/gtktooltip.c
@@ -905,7 +905,8 @@ gtk_tooltip_set_last_window (GtkTooltip *tooltip,
 
   if (window_widget &&
       window_widget != tooltip->window &&
-      gtk_widget_is_toplevel (window_widget))
+      gtk_widget_is_toplevel (window_widget) &&
+      GTK_IS_WINDOW (window_widget))
     gtk_window_set_transient_for (GTK_WINDOW (tooltip->window),
                                   GTK_WINDOW (window_widget));
   else