[trunk] Crash on loading 1.0 score with BOTH lyrics AND parts

Setup MuseScore trunk rev. 4145 both under Win XP (Qt SDK 10.04, Qt lib 4.7.0) and under Ubuntu 9.10 (Qt SDK 10.02, Qt lib 4.6.2)

Step: load a score created with MuseScore 1.0 containing BOTH lyrics AND parts (sample score attached)

Result: program crashes

Notes:

1) three scores, very small and very similar, are attached: one with both lyrics and parts, one with only lyrics, one with only parts: only the first crashes the program; neither the second or the third do; this shows that the issue derives from the combination of BOTH lyrics AND parts.

2) Crash happens at file lyrics.cpp, line 606, in function void Lyrics::layout(), during the call to sys->staff()..., because line 601:
    sys = seg->measure()->system();
returned 0.
The crash probably happens during layout process for part(s) (but this is an assumption: I could not debug the whole loading process).

M.