bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Eli Zaretskii]

> Date: Fri, 22 May 2020 10:22:56 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 41321@debbugs.gnu.org
> 
> Since the previous call to before-change-functions already used the
> same overlay markers, I suspect that the call to
> before-change-functions caused the memory to be unmapped (perhaps due
> to GC).

FTR: I am now running the 27.0.91 pretest with the patch for bug#40661
applied.  It's a long shot, since the problem here is not with
pointers to buffer text, but I just want to be sure I didn't
rediscover a complicated way to reproduce that bug ;-)