bug#41104: 28.0.50; nadvice: `find-function-library' infloops for adviced autoload fun

[Michael Heerdegen]

Hello,

in *scratch* eval this:

#+begin_src emacs-lisp
(require 'find-func)

;; we don't require 'dired so it is an autoload fun.  Then:

(advice-add 'dired
            :override
            (defun my-dired (&rest args) t))

;; And

(find-function-library 'dired)

;; infloops.
#+end_src

The problem seems be that `find-function-advised-original' unexpectedly
returns the original symbol because `advice--cd*r' returns nil in this
case.

TIA,

Michael.