bug#66589: 30.0.50; core dump in redisplay

[Eli Zaretskii <eliz@gnu.org>]

> From: Evgeny Zajcev <lg.zevlg@gmail.com>
> Date: Tue, 17 Oct 2023 21:11:40 +0300
> Cc: 66589@debbugs.gnu.org
> 
> (gdb) frame 19
> #19 0x000055ccdf1eb141 in gui_produce_glyphs (it=0x7ffef46c5660) at
> lisp.h:1179
> 1179      return make_lisp_symbol (&lispsym[index]);
> (gdb) p it->current
> $6 = {
>   pos = {
>     charpos = 10098,
>     bytepos = 14401
>   },
>   overlay_string_index = -1,
>   string_pos = {
>     charpos = -1,
>     bytepos = -1
>   },
>   dpvec_index = -1
> }
> (gdb) p current_buffer->zv
> No symbol "current_buffer" in current context.
> (gdb) p current_thread->m_current_buffer
> $7 = (struct buffer *) 0x55ccf0885fb0
> (gdb) p current_thread->m_current_buffer->zv
> $8 = 10106
> (gdb) p current_thread->m_current_buffer->text->beg[10000]@106
> $9 = "     \n    | ⮪ Yura› Позорище 🤦‍♂ у ФСБ только на Газель Хва",
> <incomplete sequence \320>
> (gdb)

Hmm... what about this:

  (gdb) frame 18
  (gdb) p current_thread->m_current_buffer->text->gpt_byte
  (gdb) p current_thread->m_current_buffer->zv_byte
  (gdb) p current_thread->m_current_buffer->text->beg[14350]@100