bug#49066: 26.3; Segmentation fault on specific utf8 string

[Eli Zaretskii]

> Date: Thu, 17 Jun 2021 16:59:42 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 49066@debbugs.gnu.org, larsi@gnus.org, mvsfrasson@gmail.com
> 
> > This is enough to cause the crash: ক‌
> > 
> > Thats #x995 followed by #x200c. Why are we trying to compose a ZWNJ?
> 
> Because #x995 is a Bengali character, and lisp/language/indian.el
> says:

Btw, I think there's a bug in those patterns: ZWJ and ZWNJ shouldn't
compose unless they are followed by a character.  See section 12.2 in
the Unicode Standard.