bug#65797: `buffer-match-p` should not use `func-arity`

[Philip Kaludercic]

Dmitry Gutov <dmitry@gutov.dev> writes:

> On 19/09/2023 11:34, Philip Kaludercic wrote:
>>> [ BTW, changing the code to use `&rest args` instead of `&optional arg`
>>>    would help for this, right?  ]
>> How come?
>
> In project.el buffer-match-p would be called without an extra
> argument, so the predicates would be called without an extra argument
> as well.
>
> That should take care of that compatibility, I think.

But what does that have to do with &rest vs &optional?