Fix ly:format for the string that contain zero (issue 300930043 by address@hidden)

[dak]

https://codereview.appspot.com/300930043/diff/1/lily/general-scheme.cc
File lily/general-scheme.cc (left):

https://codereview.appspot.com/300930043/diff/1/lily/general-scheme.cc#oldcode598
lily/general-scheme.cc:598: strncpy (ptr, results[i].c_str (),
results[i].size ());
I've suspected this one as well (basically I searched for "strn" and
"stringn" in the sources and this one was sort-of most suspicious) but I
don't see where ly:format would actually be called with the font data.

What did I overlook?

https://codereview.appspot.com/300930043/