[mutter] Check for NULL in meta_screen_tab_popup_destroy() instead of asserting

[Tomas Frydrych <tomasf src gnome org>]

commit 3e09b4a725cceb5c115bf87d5028d7cfbab53088
Author: Tomas Frydrych <tf linux intel com>
Date:   Wed Aug 26 16:26:22 2009 +0100

    Check for NULL in meta_screen_tab_popup_destroy() instead of asserting
    
    This function is getting called even when no MetaAltTabHandler object is
    installed on the screen, so we need to handle the NULL gracefully.

 src/core/screen.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/core/screen.c b/src/core/screen.c
index 59a50b0..da96bce 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -1563,7 +1563,8 @@ meta_screen_tab_popup_get_selected (MetaScreen *screen)
 void
 meta_screen_tab_popup_destroy (MetaScreen *screen)
 {
-  g_return_if_fail (screen->tab_handler != NULL);
+  if (!screen->tab_handler)
+    return;
 
   meta_alt_tab_handler_destroy (screen->tab_handler);
   g_object_unref (screen->tab_handler);