libtorc-audio: Reset audio time when creating/destroying audio device
libtorc-audio: AudioDecoder improvements

- process decoder loops at least once in case the entire stream is
buffered before the loop is started (can happen if audio setup takes a
while)
- fix 2 deadlocks in audio reconfiguration introduced with stream
locking
- don't use the stream start time in timecode calculations - it just
complicates things
- calculate audio timecodes when no pts is present