bug#65128: 30.0.50; Strange code in help-fns.el

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@posteo.net>
> Date: Mon, 07 Aug 2023 16:30:56 +0000
> 
> Hi,
> 
> I am looking at lisp/help-fns.el:describe-keymap and seeing
> 
>  (let ((sym nil))
>     (unless sym
>     ...
> 
> It looks like an oversight - sym will always be nil there.

Adding Stefan, who wrote that function.