Fix mei2hum duration parsing

[fernandoherreradelasheras]

Currently a mei file like this:

 <score>
          <scoreDef>
            <staffGrp>
              <staffDef n="1" lines="5" meter.count="4" meter.unit="4">
                <clef shape="G" line="2" />
              </staffDef>
            </staffGrp>
          </scoreDef>
          <section>
            <measure n="1">
              <staff n="1">
                <layer n="1">
                  <note dur="4" pname="c" oct="4" />
                  <note dur="4" pname="d" oct="4" />
                  <note dur="4" pname="e" oct="4" />
                  <note dur="4" pname="f" oct="4" />
                </layer>
              </staff>
            </measure>
          </section>
        </score>

produces these warnings:

Warning, replacing existing token: 4d with a null token around time 1/4 in layerindex 0
GRID STAFF: (v0:) "4e"  [] 
Warning, replacing existing token: 4e with a null token around time 1/4 in layerindex 0
GRID STAFF: (v0:) "4f"  [] 
Warning, replacing existing token: 4f with a null token around time 1/4 in layerindex 0
GRID STAFF: (v0:) ".ZZZ4e"  [] 
Warning, replacing existing token: .ZZZ4e with a null token around time 1/4 in layerindex 0
GRID STAFF: (v0:) ".ZZZ4f"  [] 
Warning, replacing existing token: .ZZZ4f with a null token around time 1 in layerindex 0
GRID STAFF: (v0:) ".ZZZ4f"  [] 
Warning, replacing existing token: .ZZZ4f with a null token around time 1 in layerindex 0

and the humdrum output gets tagged with ZZZ:

!!!OTL: Test
**kern
*part1
*staff1
*M4/4
4c
.ZZZ4d
.ZZZ4e
.ZZZ4f
=
*-

The problem seems to be that tool-mei2hum.cpp defines QUARTER_CONVERT as no-op, resulting on wrong duration for measures parsed from mei files. Uncommenting the original #define QUARTER_CONVERT * 4 fixes the issue.