BufferedStreamer.Stream treated an empty ring buffer as a momentary
underrun and answered with silence and ok. That is right while the
read-ahead is still going to deliver something, and two of its three
exit paths left it never going to: a Close, and a source returning
(0, true) in a loop. Neither set done, so the ring drained and every
call after it was silence claiming to be audio, for the life of the
process.
Nothing above this type could tell that from healthy playback. The
beep.Seq chain never ended, so the player stayed in Playing with the
button showing pause; the decoder's position never moved, so the 1 Hz
report pinned the seek bar at a constant -- and since every report
resets the bar's interpolation, the report actively suppressed the one
thing that would still have moved it. A frozen bar over a track that
was not playing, with no watchdog anywhere to notice.
Every exit now marks the stream done, and the silence fill is bounded
by a duration *and* a run of calls. It needs both. Wall clock is the
real measure, because the speaker paces itself and a stall is a
question about time -- but a caller draining in a tight loop makes
hundreds of calls in microseconds and would outrun a duration alone.
A call count alone is the opposite failure, and not a hypothetical
one: the first attempt used one and spent the whole budget before the
read-ahead goroutine had been scheduled once, ending a perfectly good
stream at sample zero and breaking TestBufferedStreamer_BasicStream.
Err is plumbed out at the same time, because a drained source and a
failed one both arrive as (0, false) and are not the same event.
Reading it is a separate change; without it there is nothing to read.
Closes#122
