[mutter/wayland] wayland-surface: Allow extension resources to be double-destroyed

[Jasper St. Pierre <jstpierre src gnome org>]

commit 2ebecc5370eb61668feff2fd8742891ca40f30fc
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Tue Nov 19 19:27:04 2013 -0500

    wayland-surface: Allow extension resources to be double-destroyed
    
    As they will be on shutdown... I'm not sure if this is a wayland-server
    bug or not, but we should guard against it anyway.

 src/wayland/meta-wayland-surface.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/wayland/meta-wayland-surface.c b/src/wayland/meta-wayland-surface.c
index 317f4fb..ebcd964 100644
--- a/src/wayland/meta-wayland-surface.c
+++ b/src/wayland/meta-wayland-surface.c
@@ -478,6 +478,10 @@ static void
 destroy_surface_extension (struct wl_resource *resource)
 {
   MetaWaylandSurfaceExtension *extension = wl_resource_get_user_data (resource);
+
+  if (extension->resource == NULL)
+    return;
+
   wl_list_remove (&extension->surface_destroy_listener.link);
   extension->surface_destroy_listener.notify = NULL;
   extension->resource = NULL;