Log Message:
musicpd: update to 0.21.18.

ver 0.21.18 (2019/12/24)
* protocol
  - work around Mac OS X bug in the ISO 8601 parser
* output
  - alsa: fix hang bug with ALSA "null" outputs
* storage
  - curl: fix crash bug
* drop support for CURL versions older than 7.32.0
* reduce unnecessary CPU wakeups

ver 0.21.17 (2019/12/16)
* protocol
  - relax the ISO 8601 parser: allow omitting field separators, the
    time of day and the "Z" suffix
* archive
  - zzip: improve error reporting
* outputs
  - jack: mark ports as terminal
  - shout: declare metadata as UTF-8
* fix build failure with -Ddatabase=false