CompositeAudioClip not compute duration

[CorrM]

The __init__ function should look something like that:

        if not any([(e is None) for e in ends]):
            self.duration = max(ends)
            self.end = max(ends)
        elif not any([(d is None) for d in [c.duration for c in self.clips]]):
            self.duration = max([c.duration for c in self.clips])
            self.end = self.duration

because the docs for clips are:

clips
      List of audio clips, which may start playing at different times or
      together. If all have their ``duration`` attribute set, the
      duration of the composite clip is computed automatically.