\balloonGrobText for ledger lines

[Werner LEMBERG]

[lilypond be08490329a22423bb2a723eea7a5cd33f3a42d8]

I was just about asking on the user list how to get a balloon text for
a ledger line (apparently, it's not possible); while preparing a MWE I
found out that the following crashes lilypond:

  \new Staff \with {
    \consists "Balloon_engraver"
  } {
    \balloonGrobText #'LedgerLineSpanner #'(1 . 0.5)
      \markup "ledger line"
        a''16
  }

gdb reports

  #0  0x000000000041e9b6 in Paper_column::get_rank() const (this=0x0) at 
./include/paper-column.hh:47
  #1  0x0000000000589f51 in Item::spanned_rank_interval() const 
(this=0x1026a90) at item.cc:191
  #2  0x000000000042af1c in Grob::less(Grob*, Grob*) (g1=0x1026a90, 
g2=0x10264b0) at grob.cc:537

as the top stack entries.


    Werner