Honor XM pattern header size

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

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

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

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