improve querying _levelN properties
improve querying _levelN properties

- use swfdec_player() functions for querying stuff
- If the level is empty, don't return a child movie

mltframework/swfdec,freedesktop-unofficial-mirror/swfdec__swfdec,mltframework/swfdec,freedesktop-unofficial-mirror/swfdec__swfdec,freedesktop-unofficial-mirror/swfdec__swfdec