Don't mess with WNDCLASS contents if class doesn't exist

reactos/lib/user32/windows

diff -u -r1.52 -r1.53
--- class.c	4 Dec 2004 22:08:29 -0000	1.52
+++ class.c	17 Dec 2004 09:56:10 -0000	1.53
@@ -1,4 +1,4 @@

-/* $Id: class.c,v 1.52 2004/12/04 22:08:29 navaraf Exp $

+/* $Id: class.c,v 1.53 2004/12/17 09:56:10 gvg Exp $

  *
  * COPYRIGHT:       See COPYING in the top level directory
  * PROJECT:         ReactOS user32.dll

@@ -170,7 +170,10 @@

   }
 
   retval = GetClassInfoExA(hInstance,lpClassName,&w);

-  RtlCopyMemory ( lpWndClass, &w.style, sizeof(WNDCLASSA) );

+  if (retval)
+  {
+    RtlCopyMemory ( lpWndClass, &w.style, sizeof(WNDCLASSA) );
+  }

   return retval;
 }