[gtk+] gdk: Don't crash when resetting cursor

[Bastien Nocera <hadess src gnome org>]

commit 779591b62fbc5ee4ebf9912a4416b655cdcf4e32
Author: Bastien Nocera <hadess hadess net>
Date:   Thu May 10 15:23:57 2012 +0100

    gdk: Don't crash when resetting cursor
    
    When the toplevel is a GdkOffscreenWindow which doesn't
    implement the set_device_cursor() vfunc.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=675809

 gdk/gdkwindow.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 2683073..b7e6a13 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -7805,7 +7805,8 @@ update_cursor (GdkDisplay *display,
    * which native window has what cursor set. */
   toplevel = get_event_toplevel (pointer_window);
   impl_class = GDK_WINDOW_IMPL_GET_CLASS (toplevel->impl);
-  impl_class->set_device_cursor (toplevel, device, cursor);
+  if (impl_class->set_device_cursor)
+    impl_class->set_device_cursor (toplevel, device, cursor);
 }
 
 static gboolean