Fix assertion failure (#2983).

diff --git a/lily/line-spanner.cc b/lily/line-spanner.cc
index f80d58132d5fc1a71067c6c44fcbce3d8b06b2d4..936a95600842c922ffe04584142e08de059e8ffb 100644 (file)
--- a/lily/line-spanner.cc
+++ b/lily/line-spanner.cc
@@ -189,7 +189,9 @@ Line_spanner::calc_bound_info (SCM smob, Direction dir)
         }
       else
         {
-          y = me->get_bound (dir)->extent (common_y, Y_AXIS).center ();
+          Interval ii = me->get_bound (dir)->extent (common_y, Y_AXIS);
+          if (!ii.is_empty())
+            y = ii.center ();
           details = scm_acons (ly_symbol2scm ("common-Y"), common_y->self_scm (), details);
         }