bug#36166: 27.0.50; Crash visiting HELLO when fringe-mode is disabled

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Tue, 11 Jun 2019 10:15:57 +0200
> 
> 
> HOME=/tmp src/emacs /tmp/HELLO
> 
> where /tmp/.emacs.d/init.el contains:
> 
> (custom-set-variables
> '(fringe-mode 0 nil (fringe))
>  )
> 
> and /tmp/HELLO is etc/HELLO with all the non-ASCII removed except for
> the line in Maldivian. I donʼt have a font that can display Maldivian.
> 
> gdb:
> 
> Thread 3 received signal SIGSEGV, Segmentation fault.
> ns_compute_glyph_string_overhangs (s=0x7ffeefbfc7e0) at nsterm.m:2941
> 2941        if (EQ (font->driver->type, Qns))
> (gdb) bt
> #0  ns_compute_glyph_string_overhangs (s=0x7ffeefbfc7e0) at nsterm.m:2941
> #1  0x0000000100039d74 in draw_glyphs (w=<optimized out>, x=562, 
> row=0x1050c5b00, area=TEXT_AREA, start=0, end=50,
>     hl=DRAW_NORMAL_TEXT, overlaps=0) at xdisp.c:27050

This appears to be NS-specific: the NS version of the
compute_glyph_string_overhangs method is very different from the X and
w32 versions, and lacks some safety devices.  (I did try the recipe on
w32, and didn't see any crashes.)

Thanks.