Without this, the compiler may optimize accesses away.

This is useful in multiple mpd instances scenario, or multiple pulse outputs defined on the same mpd instance.
It is actually a more flexible way to route flows than the "sink" parameter, letting the PulseAudio routing do its job, but with the ability to isolate routing for each output.

If not specified, the role remains like it was before this commit, ie "music"

Time to move on, two years after 2017.

Much of that is not possible when mad_header_decode() has already been
called.

release v0.21.12

The check IsSeekableCurrentSong() was added by commit
44b20024 in version 0.20.19, but it
caused a regression: by doing the branch only if the current song is
seekable, the player would restart the current song if it was not
seekable, and later the initial seek would fail; but we already know
it's not seekable, and so we should fail early.

libmad has a hard-coded maximum PCM buffer size; if we make our
output_buffer just as large, we can avoid the loop, because any
possible size will fit.

These will not be used until they are initialized in SyncAndSend().

Apparently, libmad not only inserts 529 samples of silence at the
beginning of the file, but also removes them at the end.

This solves the last piece of
https://github.com/MusicPlayerDaemon/MPD/issues/601

Closes https://github.com/MusicPlayerDaemon/MPD/issues/601

libmad requires padding the input buffer with "MAD_BUFFER_GUARD" zero
bytes at the end of the file, or else it is unable to decode the last
frame.

This fixes yet another bug which prevented this plugin from decoding
the last frame, see
https://github.com/MusicPlayerDaemon/MPD/issues/601

The Xing/LAME frame indicates how many frames there are, but that
excludes the initial Xing/LAME frame.  Therefore, it should not be
counted.

This fixes an off-by-one bug which caused the last frame to be
skipped, fixing one part of
https://github.com/MusicPlayerDaemon/MPD/issues/601

Increment "current_frame" after processing the frame.

This also fixes a bug which caused the bit rate to not update after
seeking.

Broken since commit f8bfea8b