[gtk+] Don't segfault when setting opacity on an offscreen window

[Matthias Clasen <matthiasc src gnome org>]

commit f636a2668b4a4cbacd7b7d8a5ab1efb034be9639
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Jul 9 20:05:46 2013 -0400

    Don't segfault when setting opacity on an offscreen window
    
    This was causing the treeview tests to fail.

 gdk/gdkoffscreenwindow.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/gdk/gdkoffscreenwindow.c b/gdk/gdkoffscreenwindow.c
index 86b77a1..fda8907 100644
--- a/gdk/gdkoffscreenwindow.c
+++ b/gdk/gdkoffscreenwindow.c
@@ -691,6 +691,11 @@ gdk_offscreen_window_get_scale_factor (GdkWindow *window)
 }
 
 static void
+gdk_offscreen_window_set_opacity (GdkWindow *window, gdouble opacity)
+{
+}
+
+static void
 gdk_offscreen_window_class_init (GdkOffscreenWindowClass *klass)
 {
   GdkWindowImplClass *impl_class = GDK_WINDOW_IMPL_CLASS (klass);
@@ -764,7 +769,7 @@ gdk_offscreen_window_class_init (GdkOffscreenWindowClass *klass)
   impl_class->begin_move_drag = NULL;
   impl_class->enable_synchronized_configure = gdk_offscreen_window_do_nothing;
   impl_class->configure_finished = NULL;
-  impl_class->set_opacity = NULL;
+  impl_class->set_opacity = gdk_offscreen_window_set_opacity;
   impl_class->set_composited = NULL;
   impl_class->destroy_notify = NULL;
   impl_class->register_dnd = gdk_offscreen_window_do_nothing;