mpd 0.19.3

This is a bugfix release, with the following things fixed:
* fix build failure on Mac OS X with non-Apple compilers
* protocol
  - fix "(null)" result string to "list" when AlbumArtist is disabled
* database
  - upnp: fix breakage due to malformed URIs
* input
  - curl: another fix for redirected streams
* decoder
  - audiofile: fix crash while playing streams
  - audiofile: fix bit rate calculation
  - ffmpeg: support opus
  - opus: fix bogus duration on streams
  - opus: support chained streams
  - opus: improved error logging
* fix distorted audio with soxr resampler