Robustify 'line-count lookup in clef::print-modern-tab-if-set.

diff --git a/scm/tablature.scm b/scm/tablature.scm
index ae617bd47ffef752139e4cc20f2d320f983f2ed0..8d15fceeb406b6fcf38b65344b28cecc8ca55fbc 100644 (file)
--- a/scm/tablature.scm
+++ b/scm/tablature.scm
@@ -99,7 +99,9 @@
     (if (string=? glyph "markup.moderntab")
         ;; if it is "moderntab", we'll draw it
         (let* ((staff-symbol (ly:grob-object grob 'staff-symbol))
-               (line-count (ly:grob-property staff-symbol 'line-count))
+               (line-count (if (ly:grob? staff-symbol)
+                              (ly:grob-property staff-symbol 'line-count)
+                              0))
                (staff-space (ly:staff-symbol-staff-space grob)))
 
           (grob-interpret-markup grob (make-customTabClef-markup line-count