Log Message:
libopenmpt: update to 0.5.6.

### libopenmpt 0.5.6 (2021-03-14)

 *  AMS: Avoid allocating excessive amount of memory for compressed song message
    in malformed files.
 *  S3M: Some samples or OPL patches were imported with a too high sample rate
    if module was saved with Scream Tracker 3.

 *  vorbis: Update to v1.3.7 (2020-07-04).