change the type of selection from rt_uint16_t to rt_int16_t.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@489 bbd45198-f89e-11dd-88c7-29a3b14d5316

rtgui/include/rtgui/widgets/radiobox.h

@@ -25,7 +25,8 @@ struct rtgui_radiobox
 	rt_uint8_t item_size;
 
 	char** items;
-	rt_uint16_t item_count, item_selection;
+	rt_uint16_t item_count;
+	rt_int16_t  item_selection;
 };
 typedef struct rtgui_radiobox rtgui_radiobox_t;