bug#34256: 27.0.50; Crash on draw_glyphs()

[Eli Zaretskii <eliz@gnu.org>]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Wed, 30 Jan 2019 13:22:01 -0500
> Cc: 34256@debbugs.gnu.org
> 
> - I cannot reproduce the crash in an emacs -Q session using the same Org file, or even using my full
> unaltered config (except for commenting out desktop loading).
> 
> But now I have this detailed backtrace; hopefully it helps you spot the problem:
> 
> xdisp.c:26154: Emacs fatal error: assertion failed: s->img
> 
> Thread 1 "emacs" hit Breakpoint 1, terminate_due_to_signal (sig=sig@entry=6,
>     backtrace_limit=backtrace_limit@entry=2147483647) at emacs.c:370
> 370     {
> (gdb) bt
> #0  terminate_due_to_signal (sig=sig@entry=6, backtrace_limit=backtrace_limit@entry=2147483647) at
> emacs.c:370
> #1  0x00000000005a1622 in die (msg=msg@entry=0x67dc2c "s->img", file=file@entry=0x67dbaa "xdisp.c",
> line=line@entry=26154) at alloc.c:7453
> #2  0x00000000004378fe in fill_image_glyph_string (s=s@entry=0x7fffffff7aa0) at xdisp.c:26154
> #3  0x00000000004708cf in draw_glyphs (w=w@entry=0x13fa4e0, x=44, row=0x234ba50,
> area=area@entry=TEXT_AREA, start=<optimized out>, start@entry=0, end=end@entry=6,
> hl=DRAW_NORMAL_TEXT, overlaps=0)
>     at xdisp.c:26841

This says Emacs was trying to display an image, but what image is
that?  Where did it come from?  And could it be that the new native
image scaling is the reason for this (i.e., was the image supposed to
be resized)?  Hmm, but you built with ImageMagick, which AFAIU means
the native  resizing code should not be invoked...

> - The Org file/buffer seen when this crash happens displays inline images.

Please show the relevant parts of the file anyway.

Also, in this callstack frame:

  #2  0x00000000004378fe in fill_image_glyph_string (s=s@entry=0x7fffffff7aa0) at xdisp.c:26154

please show the full contents of s->first_glyph.  Like this:

  (gdb) frame 2
  (gdb) p *s->first_glyph