control/media_instance.c: Listen to the variable changes.

src/control/media_instance.c

@@ -395,6 +395,8 @@ void libvlc_media_instance_play( libvlc_media_instance_t *p_mi,
                                          p_mi->p_md->p_input_item );
     p_mi->i_input_id = p_input_thread->i_object_id;
 
+    var_AddCallback( p_input_thread, "state", input_state_changed, p_mi );
+
     /* will be released in media_instance_release() */
     vlc_object_yield( p_input_thread );