bug#53809: 29.0.50; fatal error: assertion failed: string_immovable_p (bytestr)

[Eli Zaretskii <eliz@gnu.org>]

> From: Gregor Zattler <telegraph@gmx.net>
> Cc: 53809@debbugs.gnu.org
> Date: Mon, 07 Feb 2022 15:12:40 +0100
> 
> Lisp Backtrace:
> "gnus-alias-init" (0xffffacc0)
> "progn" (0xffffaea8)
> "condition-case" (0xffffb0f8)
> "progn" (0xffffb238)
> 0x5cc02ee0 Lisp type 3
> "eval-after-load" (0xffffb590)
> "condition-case" (0xffffb768)
> "load-with-code-conversion" (0xffffbca8)
> "load-file" (0xffffc068)
> "org-babel-load-file" (0xffffc238)
> "mapc" (0xffffc3b0)
> "let" (0xffffc528)
> "load-with-code-conversion" (0xffffca08)
> "load" (0xffffcde8)
> "startup--load-user-init-file" (0xffffcfb8)
> "command-line" (0xffffd180)
> "normal-top-level" (0xffffd290)
> (gdb) fr 2
> #2  0x00005555558948b2 in exec_byte_code (bytestr=XIL(0x55555cc35654), vector=XIL(0x55555b5dabc5), maxdepth=make_fixnum(3), args_template=0, nargs=0, args=0x0) at bytecode.c:361
> 361       eassert (string_immovable_p (bytestr));
> (gdb) p bytestr
> $1 = XIL(0x55555cc35654)
> (gdb) xstring
> $2 = (struct Lisp_String *) 0x55555cc35650
> "\300\301\302\"\207"
> (gdb)

Thanks.

CC'ing Mattias, who added that assertion about 2 weeks ago.  Sounds
like it is sometimes violated?