French beams over rests cause segfault

[Jean Menezes da Rocha]

> I'm not top posting.

Hello,

I may have stumbled upon a bug. Everytime a group of beamed notes ends with a 
rest, if I enable french-beaming the compilation is stopped by a segmentation 
fault.

this example:

\version "2.19.30"

\relative c'' {
  \override Stem.french-beaming = ##t
  c16[ d e r]
}

always produces a segfault, while

\version "2.19.30"

\relative c'' {
  \override Stem.french-beaming = ##t
  c16[ d e f]
}

does not. Starting the group with a rest won't be harmful, either. Only rests 
ending a group of 'french-beamed' notes will call the segfault.

Thanks for your attention!