MusicXML export (partStaff) drops clef-octave-change on the floor #1333
Description
music21 version
8.0.0a3
Problem summary
I end up with a treble clef in the exported MusicXML when it should be a TrebleV8 clef.
Steps to reproduce
s=converter.parse('''<?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
<!DOCTYPE score-partwise PUBLIC "-//Recordare//DTD MusicXML 0.6b Partwise//EN"
"http://www.musicxml.org/dtds/partwise.dtd">
<score-partwise>
<identification>
<miscellaneous>
<miscellaneous-field name="description">Polymeter on a grand staff</miscellaneous-field>
</miscellaneous>
</identification>
<part-list>
<score-part id="P1">
<part-name>MusicXML Part</part-name>
</score-part>
</part-list>
<part id="P1">
<measure number="1">
<attributes>
<divisions>96</divisions>
<key><fifths>0</fifths></key>
<time number="1"><beats>4</beats><beat-type>4</beat-type></time>
<time number="2"><beats>2</beats><beat-type>2</beat-type></time>
<staves>2</staves>
<clef number="1"><sign>G</sign><line>2</line></clef>
<clef number="2">
<sign>G</sign>
<line>2</line>
<clef-octave-change>-1</clef-octave-change>
</clef>
</attributes>
<note>
<pitch><step>F</step><octave>4</octave></pitch>
<duration>384</duration>
<voice>1</voice>
<type>whole</type>
<staff>1</staff>
</note>
<backup><duration>384</duration></backup>
<note>
<pitch><step>B</step><octave>2</octave></pitch>
<duration>384</duration>
<voice>2</voice>
<type>whole</type>
<staff>2</staff>
</note>
</measure>
</part>
</score-partwise>
'''
SX = musicxml.m21ToXml.ScoreExporter(s)
root = SX.parse()
m1 = root.find('part/measure')
SX.dump(m1)
print('Notice how the <clef-octave-change>-1</clef-octave-change> is gone from clef #2')