adding note to bassclef crashes

Musescore revision 00f6a59 (under linux x86-64)

Opening the attached score file and going into N-mode, then trying to add a note to bass clef will crash the program.

I see three possible bugs here:

1) The musescore file has somehow got corrupted during a previous session (which I have no further debugging how I got there).

2) Musescore crashes when dealing with a corrupted score file (not graceful).

3) The scorefile is valid but somehow triggers a bug when adding a note.