macosx: fixed corner-case crash

modules/gui/macosx/embeddedwindow.m

 /*****************************************************************************
  * embeddedwindow.m: MacOS X interface module
  *****************************************************************************
- * Copyright (C) 2005-2008 the VideoLAN team
+ * Copyright (C) 2005-2011 the VideoLAN team
  * $Id$
  *
  * Authors: Benjamin Pracht <bigben at videolan dot org>
@@ -425,21 +425,23 @@
     vout_thread_t *p_vout = getVout();
     BOOL blackout_other_displays = config_GetInt( VLCIntf, "macosx-black" );
 
+    if( p_vout )
         screen = [NSScreen screenWithDisplayID:(CGDirectDisplayID)var_GetInteger( p_vout, "video-device" )];
 
     [self lockFullscreenAnimation];
 
     if (!screen)
     {
-        msg_Dbg( p_vout, "chosen screen isn't present, using current screen for fullscreen mode" );
+        msg_Dbg( VLCIntf, "chosen screen isn't present, using current screen for fullscreen mode" );
         screen = [self screen];
     }
     if (!screen)
     {
-        msg_Dbg( p_vout, "Using deepest screen" );
+        msg_Dbg( VLCIntf, "Using deepest screen" );
         screen = [NSScreen deepestScreen];
     }
 
+    if( p_vout )
         vlc_object_release( p_vout );
 
     screen_rect = [screen frame];