While libsndfile doesn't like partial reads in the middle of a file
(see commit 95ac6071b9), it allows partial reads at the end of a file.
It doesn't pay attention to the file size when issuing a read.
Commit ecb67a1ed1 (MPD 0.18.12) was a regression: previously,
partial reads at the end of a file were possible, but switching to
decoder_read_full() made this an error condition. This way, a portion
at the end of each file was lost, leading to corruption with gapless
playback (https://github.com/MusicPlayerDaemon/MPD/issues/936).
This fix switches to the newly introduced function
decoder_read_much(), which does the same as the code before commit
ecb67a1ed1.
Closes https://github.com/MusicPlayerDaemon/MPD/issues/936
0aa0ffb67b