Parts with lyrics causes crash

Steps to reproduce bug
1. Open attached file: "Lyrics.mscz" in nightly build

--> Crash

Workaround:
1. Open "Lyrics.mscz" in MuseScore 1.0
2. File > Parts
3. Delete "Soprano" part
4. File > Save

--> File now opens in nightly build

MuseScore version: r. 4051 nightly build

(Operating System: Windows 7)

first reported by robert leleu: http://musescore.org/en/node/9445