Audio export fails with "list index out of range"

[Bentroen]

Audio export fails with the following error message:

This bug affects NBS 3.10.0. A possible workaround is to change something in the last layer with a note block (e.g. rename, lock etc.)

This is a bug in nbswave and its progress is being tracked here: OpenNBS/nbswave#5

[Bentroen]

Fixed in 998c78f