Fix issue 3868: line-breaking makes short lines

Two simple fixes:
1) Always have some stretchability between notes
2) If there _is_ a completely unstretchable line, shorter than the line-width,
   score it as a bad fit, not as a perfect fit (report large forces for stiff lines).

Either one would fix the problem; both seem to be good to have in the code.

1 files changed, 1 insertions, 1 deletions

diff --git a/lily/simple-spacer.cc b/lily/simple-spacer.cc
index f3aee71997..2eb545756f 100644
--- a/lily/simple-spacer.cc
+++ b/lily/simple-spacer.cc
@@ -193,7 +193,7 @@ Simple_spacer::expand_line ()
     inv_hooke += springs_[i].inverse_stretch_strength ();
 
   if (inv_hooke == 0.0) /* avoid division by zero. If springs are infinitely stiff */
-    return 0.0;         /* anyway, then it makes no difference what the force is */
+    inv_hooke = 1e-6;   /* then report a very large stretching force */
 
   assert (cur_len <= line_len_);
   return (line_len_ - cur_len) / inv_hooke + force_;