fix illegal MIDI event message during import

This happens when reimporting a MIDI file taken from Ardour, which
has sequencer specific data (namely, note-IDs). In that case
SMF::read_event() returns zero to indicate a meta event that we
should or could be interested in. For import, we are not interested,
hence the ignored_note_id variable

libs/ardour/import.cc

@@ -405,6 +405,11 @@ write_midi_type0_data_to_one_file (Evoral::SMF* source, ImportStatus& status, si
 				continue;
 			}
 
+			if (ret == 0) {
+				/* set note id, but we ignored it */
+				continue;
+			}
+
 			if (size > bufsize) {
 				bufsize = size;
 			}