Programming error with tempoHideNote = ##t

[Neil Puttock]

Hi Reinhold,

There's a problem using tempoHideNote if there's no markup text, since
it returns SCM_BOOL_F to the engraver, resulting in a programming
error:

\set Score.tempoHideNote = ##t
\tempo 4 = 60

returns `Object is not a markup.'

I've attached a patch which gets rid of the error message, but I'm not
sure whether it's the best method method for fixing this. What do you
think?

Incidentally, I wonder whether ly:context-property should have the
option of returning a default, like ly:grob-property...

Cheers,
Neil

0001-Ensure-format-metronome-markup-always-returns-markup.patch
Description: Text Data