Another attempt to solve bug #14062 with assertion violations on MS-Windows.

 src/w32fns.c (w32_wnd_proc): Don't call WINDOW_HEADER_LINE_HEIGHT
 unless we know that the window w is a leaf window.  Another
 attempt at solving bug#14062.

src/ChangeLog

+2013-05-14  Eli Zaretskii  <eliz@gnu.org>
+
+	* w32fns.c (w32_wnd_proc): Don't call WINDOW_HEADER_LINE_HEIGHT
+	unless we know that the window w is a leaf window.  Another
+	attempt at solving bug#14062.
+
 2013-05-14  Jan Djärv  <jan.h.d@swipnet.se>
 
 	* nsfont.m (ns_spec_to_descriptor): Retain and autorelease

src/w32fns.c

@@ -3183,8 +3183,9 @@ w32_wnd_proc (HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 	  form.ptCurrentPos.y = w32_system_caret_y;
 
 	  form.rcArea.left = WINDOW_TEXT_TO_FRAME_PIXEL_X (w, 0);
-	  form.rcArea.top = (WINDOW_TOP_EDGE_Y (w)
-			     + WINDOW_HEADER_LINE_HEIGHT (w));
+	  form.rcArea.top = WINDOW_TOP_EDGE_Y (w);
+	  if (BUFFERP (w->contents))
+	    form.rcArea.top += WINDOW_HEADER_LINE_HEIGHT (w);
 	  form.rcArea.right = (WINDOW_BOX_RIGHT_EDGE_X (w)
 			       - WINDOW_RIGHT_MARGIN_WIDTH (w)
 			       - WINDOW_RIGHT_FRINGE_WIDTH (w));