bug#30182: Update

[Eli Zaretskii]

> Date: Mon, 29 Jan 2018 11:04:18 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: Eli Zaretskii <eliz@gnu.org>, 30182@debbugs.gnu.org
> 
>  > (gdb) bt full
> [...]
>  >          result_len = 4
> [...]
>  > (gdb) p old_len_0
>  > $1 = 5
>  > (gdb) p new_len_0
>  > $2 = 5
> 
> This means that Fmake_list doesn't play a rôle here and a timer is
> added in a very constant fashion in between setting result_len to 4 on
> line 636 and making the list on line 646 of fns.c.  Crazy.

Ideas for how this could happen are welcome.