am 493941b8: Allow creation of an audio effect on a session with no audio tracks.

Merge commit '493941b8d8a12ee843d9823c0177f8005a7be54f' into gingerbread-plus-aosp

* commit '493941b8d8a12ee843d9823c0177f8005a7be54f':
  Allow creation of an audio effect on a session with no audio tracks.