bug#37786: 26.3; Emacs crashes when calling function to decode string

[Robert Pluim]

>>>>> On Thu, 17 Oct 2019 06:22:10 +0200, Lars Ingebrigtsen <larsi@gnus.org> 
>>>>> said:

    Lars> Allen Li <darkfeline@felesatra.moe> writes:
    >> The following expression, when evaluated in emacs -Q, causes emacs to
    >> crash and dump core:
    >> 
    >> (mail-decode-encoded-word-string
    >> #("=?UTF-8?B?4pyoUERYQ09OIFNBTEXinKggRW5qb3kgU3BlY2lhbCBPZmZlcnMg?=
    >> =?UTF-8?B?V2hpbGUgWW91IFdhaXQh?=" 0 64 (ws-butler-chg chg) 64 65
    >> (ws-butler-chg chg) 65 97 (ws-butler-chg chg)))

    Lars> I'm unable to reproduce this in Emacs 27 or Emacs 26.3.

    Lars> Could you do this under gdb and post the backtrace?

Probably font-related. I suspect "C-x 8 RET 2728" will cause the same
crash for OP.

Robert