bug#40409: 27.0.90; void variable n-reb

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Date: Sat, 04 Apr 2020 12:52:25 -0400
> Cc: 40409@debbugs.gnu.org
> 
> The code causing this was added by [1: c1234ca9c3] (from Bug#6347), so
> it's a regression since 26.3.
> 
> The problem seems to be that the initial binding of n-reb is missing,
> and also that the code assumes dynamic binding (using symbol-value and
> set on n-reb).  I would suggest the following patch:

Thanks, please push this to emacs-27.