b=995690 correct mLastTickWritten to only advance when not blocked r=roc

mLastTickWritten and offset are stream positions, which do not advance when
the stream is blocked.

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extra : transplant_source : %15%7B%E5%E9.%89%BC%1E%F8%92%FD%3D%CB%10%FC%AD%EAT%90-
b=995690 don't advance audio output stream position 1 tick beyond what has been produced r=roc

This may result in repeating a sample sometimes due to rounding effects, but
that should only happen once per unblocked sequence of track frames.

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extra : transplant_source : %0C%E9%A4jq%286%96%B1%A9%AE%9F%1Cr%DCK%8F%AF%92i