bug#60161: [PATCH] Allow customising windmove user options with an empty prefix

[Eli Zaretskii]

> From: Philip Kaludercic <philipk@posteo.net>
> Date: Sat, 17 Dec 2022 15:04:41 +0000
> 
> I just switched to setopt, and noticed a few errors.  Among these was
> `windmove-default-keybindings', which didn't want to set
> 
>   (setopt windmove-default-keybindings '(nil . nil))
> 
> while
> 
>   (setopt windmove-default-keybindings '("C-c" . nil))
> 
> is allowed.  The mistake appears to be that the option type is
> misconfigured, and believes the car must be a keybinding, which hasn't
> been the case since Emacs 28.  The patch below updates the type,
> resolving this issue.

Thanks, please install on the release branch.