Log Message:
libopenmpt: update to 0.6.9.

### libopenmpt 0.6.9 (2023-03-05)

 *  [**Bug**] An exception could be thrown during rendering when trying to
    access the release node of an empty envelope.

 *  The fix for the OPL cutoff bug introduced in libopenmpt 0.6.7 was
    incomplete.
 *  ULT: Offset commands exceeding 65535 samples were sometimes not imported
    correctly even if there was room for them.
 *  After seeking with seek.sync_samples=1, the filter settings of playing notes
    were not updated since libopenmpt 0.6.7.
 *  Loading of and seeking inside (malformed) modules with thousands of short
    sub-songs has been sped up.