Fix fallout from 2012-08-01T05:11:36Z!dmantipov@yandex.ru that introduced WVAR.

 src/xdisp.c (try_window_id): Use WVAR in IF_DEBUG code.

src/ChangeLog

+2012-08-01  Eli Zaretskii  <eliz@gnu.org>
+
+	* xdisp.c (try_window_id): Use WVAR in IF_DEBUG code.
+
 2012-08-01  Glenn Morris  <rgm@gnu.org>
 	* s/msdos.h: Remove file.

src/xdisp.c

@@ -17834,8 +17834,8 @@ try_window_id (struct window *w)
   else
     abort ();
-  IF_DEBUG (debug_end_pos = XFASTINT (w->window_end_pos);
-	    debug_end_vpos = XFASTINT (w->window_end_vpos));
+  IF_DEBUG (debug_end_pos = XFASTINT (WVAR (w, window_end_pos));
+	    debug_end_vpos = XFASTINT (WVAR (w, window_end_vpos)));
   /* Record that display has not been completed.  */
   WVAR (w, window_end_valid) = Qnil;