bug#31180: 25.3; latex and 6x13 font

[Bruno Deremble]

Hi,

I am experiencing issues with emacs (25.3.1) and latex files.

If I set my font to
(set-default-font "6x13")

any file .tex that contains a math subscript (e.g.: $b_d$) will crash
emacs. A possible workaround that I found is to use
(setq font-latex-fontify-script nil)

but it used to work in earlier versions of emacs.
other fonts are working fine.

thank you

bruno