Log Message:
libopenmpt: update to 0.5.13.

### libopenmpt 0.5.13 (2021-11-14)

 *  [**Bug**] Fixed various undefined behaviour found with ubsan.

 *  IMF: Change envelope interpretation to be more like in XM instead of IT and
    tighten header validation.
 *  MED: Some samples had a ping-pong loop when there should be no loop at all.
 *  MT2: Ignore incorrect drums chunk size in early MT2 files
    (fixes e.g. "A little Rock" by Csumi).
 *  MT2: Work around initial master volume of 0 used in some files that apply a
    fade-in a the song start using track automation that would stay silent
    forever otherwise (track automation is currently not supported).
 *  OKT: Apply portamento on every tick.

 *  mpg123: Update to v1.29.2 (2021-10-23).