bug#29632: 25.3; Core dump after changing fonts

[Eli Zaretskii]

> From: Thomas Morgan <tlm@ziiuu.com>
> Date: Sat, 09 Dec 2017 16:34:09 -0500
> 
> I started emacs with `emacs -Q', entered the following in *scratch*,
> and evaluated with C-M-x.
> 
>   (progn
>     (create-fontset-from-fontset-spec
>      "-*-Liberation 
> Mono-normal-normal-normal-*-*-*-*-*-m-0-fontset-liberation")
>     (set-fontset-font "fontset-liberation" 'unicode-bmp "Freemono")
>     (set-face-font 'default "fontset-liberation")
>     (font-at 0 nil "ɏ")       ; 0x024F: LATIN SMALL LETTER Y WITH STROKE
>     (set-fontset-font "fontset-auto1" 'unicode-bmp "Freemono")
>     (font-at 0 nil "ɐ"))      ; 0x0250: LATIN SMALL LETTER TURNED A
> 
> This caused a core dump:
> 
>   Fatal error 11: Segmentation fault

Thanks, fixed for Emacs 26.