Fix use of uninitialized variable (backport from trunk).

* xdisp.c (note_mouse_highlight): Initialize `part', to avoid a
possible random value that matches one of those tested as
condition to clear the mouse face.

src/ChangeLog

+2012-01-09  Eli Zaretskii  <eliz@gnu.org>
+
+	* xdisp.c (note_mouse_highlight): Initialize `part', to avoid a
+	possible random value that matches one of those tested as
+	condition to clear the mouse face.
+
 2012-01-09  YAMAMOTO Mitsuharu  <mituharu@math.s.chiba-u.ac.jp>
 
 	* dispnew.c (scrolling_window): Truncate overlaps in copy

src/xdisp.c

@@ -23484,7 +23484,7 @@ note_mouse_highlight (f, x, y)
      int x, y;
 {
   Display_Info *dpyinfo = FRAME_X_DISPLAY_INFO (f);
-  enum window_part part;
+  enum window_part part = ON_NOTHING;
   Lisp_Object window;
   struct window *w;
   Cursor cursor = No_Cursor;