rework code to allow passing numbers as levels in MovieClipLoader.loadClip()
rework code to allow passing numbers as levels in MovieClipLoader.loadClip()

This breaks a testcase

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