The MAD decoder will not decode the final frame in an mp3 stream unless
it has a small amount of padding afterwards (MAD_BUFFER_GUARD bytes,
actually 8). Without this, it loses sync before returning any decoded
data from the final frame. The result is that the imported audio is
truncated by up to 1152 samples.
This commit addresses that by using a final round of input callback
calls to provide the last MAD_BUFFER_GUARD bytes after the underlying
file has reached eof. The logic is based on madplay.
30eaa0d52c