fixed crash on shutdown

reactos/subsys/win32k/ntuser

diff -u -r1.66 -r1.67
--- winsta.c	20 Nov 2004 16:46:06 -0000	1.66
+++ winsta.c	21 Nov 2004 13:02:02 -0000	1.67
@@ -16,7 +16,7 @@

  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  *

- *  $Id: winsta.c,v 1.66 2004/11/20 16:46:06 weiden Exp $

+ *  $Id: winsta.c,v 1.67 2004/11/21 13:02:02 weiden Exp $

  *
  *  COPYRIGHT:        See COPYING in the top level directory
  *  PROJECT:          ReactOS kernel

@@ -806,7 +806,7 @@

    * just a temporary hack, this will be gone soon
    */
   

-  if(PsGetWin32Thread()->Desktop != NULL)

+  if(PsGetWin32Thread() != NULL && PsGetWin32Thread()->Desktop != NULL)

   {
     WinStaObj = PsGetWin32Thread()->Desktop->WindowStation;
     ObReferenceObjectByPointer(WinStaObj, KernelMode, ExWindowStationObjectType, 0);