see also https://github.com/stump/libsmf/pull/7
* Fix validity checks of escaped data
* Handle non-EOT-terminated tracks.
* Fix buffer overflow on tempo change event
* Fix memory leaks in case loading fails
* Fix a logic errors in extract_escaped_event()
* Fix the assertion problem `is_sysex_byte(status)`
* Make libsmf more tolerant to malformed MIDI files.
(fixes import of files generated by NoteEdit)
