Grand staff label

[rettinghaus]

Grand staff labels are directed to staffDef labels but should go to staffGrp

<scoreDef meter.count="4" meter.unit="4" page.botmar="12.7mm" page.height="297mm" page.leftmar="12.7mm" page.rightmar="12.7mm" page.topmar="12.7mm" page.width="210mm" ppq="256">
  <staffGrp>
    <staffGrp n="1" symbol="brace">
      <staffDef clef.line="2" clef.shape="G" key.mode="major" key.sig="0" label="Piano" lines="5" n="1" xml:id="sd1"/>
      <staffDef clef.line="4" clef.shape="F" key.mode="major" key.sig="0" label="Piano" lines="5" n="2" xml:id="sd2"/>
    </staffGrp>
  </staffGrp>
</scoreDef>