Reset frequency envelope index on new instrument

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Also dump filter cutoff in mixer data

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Add OpenMPT CarryNNA test case

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update changelog

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>