Don't call event handlers for events which haven't been registered.

event.c

@@ -62,7 +62,8 @@ void event_dispatch(void)
 
 	if (event_get(&event)) {
 		event_clear(event);
-		(event_handler_table[event])();
+		if (event_handler_table[event] != NULL)
+			(event_handler_table[event])();
 	}
 }