robustness: don't inspect possibly empty vector.

diff --git a/lily/beaming-pattern.cc b/lily/beaming-pattern.cc
index 542ce8e455c61f6191a48c7a4d040948abd61285..87cfaf73dc39d99d39f1ee4ac7cfb6b3d76f589f 100644 (file)
--- a/lily/beaming-pattern.cc
+++ b/lily/beaming-pattern.cc
@@ -163,13 +163,16 @@ Beaming_pattern::beamify (Context *context)
             && group_starts[j+1] <= infos_[i].start_moment_)
        j++;
 
-      infos_[i].group_start_ = group_starts[j];
+      if (j < group_starts.size ())
+       infos_[i].group_start_ = group_starts[j];
+      
       infos_[i].beat_length_ = beat_length;  
       while (k + 1 < beat_starts.size() 
             && beat_starts[k+1] <= infos_[i].start_moment_)
        k++;
 
-      infos_[i].beat_start_ = beat_starts[k];
+      if (k < beat_starts.size())
+       infos_[i].beat_start_ = beat_starts[k];
     }
   
   beamify (subdivide_beams);