Do not dereference NULL pointers.

Modified: trunk/reactos/subsys/win32k/ntuser/winpos.c

--- trunk/reactos/subsys/win32k/ntuser/winpos.c	2005-07-26 22:21:02 UTC (rev 16762)
+++ trunk/reactos/subsys/win32k/ntuser/winpos.c	2005-07-26 22:40:03 UTC (rev 16763)
@@ -145,6 +145,14 @@

   {
     Old = Wnd;
     IntLockRelatives(Old);

+    if (Old->NextSibling == NULL)
+    {
+      Wnd = NULL;
+      IntUnLockRelatives(Old);
+      if (Old != Window)
+        IntReleaseWindowObject(Old);
+      break;
+    }

     Wnd = IntGetWindowObject(Old->NextSibling->Self);
     IntUnLockRelatives(Old);
     if (Old != Window)