bug#51010: 29.0.50; python completion breaks upon non-trivial rl config

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Sat, 30 Oct 2021 09:09:24 -0700
> Cc: 51010@debbugs.gnu.org, Augusto Stoffel <arstoffel@gmail.com>
> 
> Your below patch LGTM, but I would like confirmation from Eli or Lars
> if they think it is safe enough for emacs-28, or if they prefer that it
> should go to master.

I don't know enough to decide whether this change is safe enough.

Is this a recent problem, or did we always behave like that?  If the
latter, I prefer to install this on master.

Thanks.