[mutter] restart: Make meta_restart() work without a message

[Rui Matos <rtcm src gnome org>]

commit 7ed14e0ee867be5d8c21425097bac3d11720ab28
Author: Rui Matos <tiagomatos gmail com>
Date:   Thu Jun 9 19:07:15 2016 +0200

    restart: Make meta_restart() work without a message
    
    In some cases there's no meaningful message to show.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=739178

 src/core/restart.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/core/restart.c b/src/core/restart.c
index f01464c..1fa1c88 100644
--- a/src/core/restart.c
+++ b/src/core/restart.c
@@ -103,7 +103,7 @@ restart_message_painted (gpointer data)
 
 /**
  * meta_restart:
- * @message: message to display to the user.
+ * @message: (allow-none): message to display to the user, or %NULL
  *
  * Starts the process of restarting the compositor. Note that Mutter's
  * involvement here is to make the restart visually smooth for the
@@ -126,7 +126,7 @@ meta_restart (const char *message)
     MUTTER_LIBEXECDIR "/mutter-restart-helper", NULL
   };
 
-  if (meta_display_show_restart_message (display, message))
+  if (message && meta_display_show_restart_message (display, message))
     {
       /* Wait until the stage was painted */
       clutter_threads_add_repaint_func_full (CLUTTER_REPAINT_FLAGS_POST_PAINT,