[test] Fix test for IT old instrument loader

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Correctly set the number of tracks for IT modules

In previous versions the number of tracks was overestimated because
effects in disabled channels are to be processed. Change the loader to
scan all patterns and set the correct number of tracks before actually
loading track data.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Add test for IT format loader

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

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