MusicXML export strips key signatures with 0 accidentals
OS: macOS 10.14, Arch.: x86_64, MuseScore version (64-bit): 220.127.116.1133 (3.3 RC), revision: d3bff12
Description of issue
MusicXML export removes key signatures with 0 accidentals before generating the MusicXML. This means that even with the mode enhancements introduced in #271505: Allow user to set mode along with key signature, there is no way to export a key signature of A minor, D Dorian, or any other 0-accidental signature (except C major) to MusicXML. MuseScore's MusicXML export support is otherwise pretty good, so the fact that there's no way to get it to write a key signature of A minor to a MusicXML file is a pretty big problem.