[metacity] Fix crash with --sync option

[Thomas James Alexander Thurman <tthurman src gnome org>]

commit 6114cd8e88a0973b0adf4ca3ebb4e9357856c71c
Author: Owen W. Taylor <otaylor fishsoup net>
Date:   Tue May 25 13:24:42 2010 -0400

    Fix crash with --sync option
    
    If the display hasn't been initialized yet, just change the
    start variable and don't update the display.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=618613

 src/core/display.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/core/display.c b/src/core/display.c
index 429230d..4c7b4c0 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -4002,8 +4002,8 @@ meta_set_syncing (gboolean setting)
   if (setting != is_syncing)
     {
       is_syncing = setting;
-
-      XSynchronize (meta_get_display ()->xdisplay, is_syncing);
+      if (meta_get_display ())
+        XSynchronize (meta_get_display ()->xdisplay, is_syncing);
     }
 }