Fix offset effect bug compatibility

Only the mod event reader should test for Protracker 1.x offset bug
compatibility.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix XM invalid offset handling

From the OpenMPT test cases (3xx-no-old-samp.xm): "An offset effect that
points beyond the sample end should stop playback on this channel."

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

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Add OpenMPT 3xx tests

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

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