make-musicglyph-markup puzzle

[Dan Eble]

I’m having trouble figuring out how to make this function fall back on another 
time signature style (make-simple-numbered-time-signature-markup fraction) if 
the requested glyph is not present.

(define-public (make-glyph-time-signature-markup style fraction)
    (make-musicglyph-markup (string-append
                             “timesig.”
                             (symbol->string style)
                             (number->string (car fraction))
                             (number->string (cdr fraction)))))

Using this function as-is, there is a warning that no symbol is found, and no 
time signature of any kind is printed.  The code in master prints a numbered 
time signature if no symbol is found.  Is it worth trying to preserve the 
current behavior?

Thanks,
— 
Dan