Set correct error code, IsWindow() depends on this

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

--- trunk/reactos/subsys/win32k/ntuser/window.c	2005-09-18 18:59:59 UTC (rev 17921)
+++ trunk/reactos/subsys/win32k/ntuser/window.c	2005-09-18 21:48:56 UTC (rev 17922)
@@ -3233,6 +3233,7 @@

 
    if (!(Window = UserGetWindowObject(hWnd)))
    {

+      SetLastWin32Error(ERROR_INVALID_WINDOW_HANDLE);

       return 0;
    }