Fix pan effect filter in protracker loader

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
IT sets pan on either note or instrument event

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Extend setpan test to ST3 and IT modes

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Remove masterpan test

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