Ottavation markups

[Jean Abou Samra]

   Hi,

   The recent possibility to define ottavation markups introduced a bug
   when exporting to MIDI.

   For example,
   \version "2.21.0" % compiled with HEAD being
   ede0457988716a5e6fa0dd1757db0ebd96107bbc
   \score {
   { \ottava 1 c'1 }
   \midi { }
   }
   will trigger the warning
   Could not find ottavation markup for 1 octaves up.
   CCing Malte Meyne since he's the author of the patch that introduced
   the warning -- see
   http://lilypond.1069038.n5.nabble.com/Add-user-definable-ottavation-mar
   kups-issue-568970043-by-lilypond-maltemeyn-de-tc223988.html

   The MIDI output is fine though.

   Regards,

   Jean Abou Samra