[test] Add OpenMPT XM E90 test case

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix IT unmapped sample parsing

If an event has a note and instrument that map to an invalid sample, ignore
the note but store the instrument for future events. See OpenMPT test cases
NoMap.it and gxsmp.it.

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

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Add OpenMPT IT ins-flt-porta-reset test case

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