bug#72203: 31.0.50; browse-url-emacs (url-file-handler) errors when eglot is loaded

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 20 Jul 2024 00:56:38 +0000
> From:  Nick OBrien via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Steps to reproduce:
> 
>     emacs -Q
> 
>     (require 'eglot)
>     (setq debug-on-error t)
>     (browse-url-emacs "https://www.gnu.org/licenses/gpl-3.0.txt")
> 
> There is an error, but after the gpl-3.0.txt buffer is populated.  I got
> this backtrace (with long arguments manually replaced with ...):
> 
>     Debugger entered--Lisp error: (void-function nil)
>       nil(...)
>       url-directory-files("https://www.gnu.org/licenses/" nil ... t nil)
>       apply(url-directory-files ("https://www.gnu.org/licenses/" nil ... t nil))
>       url-file-handler(directory-files "https://www.gnu.org/licenses/" nil ... t nil)
>       directory-files("https://www.gnu.org/licenses/" nil ... t)
>       #f(compiled-function (d) #<bytecode 0x183c21e239c1e2a3>)("https://www.gnu.org/licenses/")
>       locate-dominating-file("https://www.gnu.org/licenses/" #f(compiled-function (d) #<bytecode 0x183c21e239c1e2a3>))
>       project-try-vc("https://www.gnu.org/licenses/")
>       run-hook-with-args-until-success(project-try-vc "https://www.gnu.org/licenses/")
>       project--find-in-directory("https://www.gnu.org/licenses/")
>       project-current()
>       eglot--current-project()
>       eglot-current-server()
>       eglot--maybe-activate-editing-mode()
>       run-hooks(after-change-major-mode-hook)
>       run-mode-hooks(text-mode-hook)
>       text-mode()
>       set-auto-mode-0(text-mode nil)
>       set-auto-mode--apply-alist(... nil nil)
>       set-auto-mode()
>       normal-mode(t)
>       after-find-file(nil t)
>       find-file-noselect-1(#<buffer gpl-3.0.txt> "https://www.gnu.org/licenses/gpl-3.0.txt" nil nil "https://www.gnu.org/licenses/gpl-3.0.txt" (nil nil))
>       find-file-noselect("https://www.gnu.org/licenses/gpl-3.0.txt" nil nil nil)
>       find-file-other-window("https://www.gnu.org/licenses/gpl-3.0.txt")
>       browse-url-emacs("https://www.gnu.org/licenses/gpl-3.0.txt")
>       (progn (browse-url-emacs "https://www.gnu.org/licenses/gpl-3.0.txt"))
>       eval((progn (browse-url-emacs "https://www.gnu.org/licenses/gpl-3.0.txt")) t)
>       elisp--eval-last-sexp(nil)
>       #f(compiled-function () #<bytecode 0x29ba0505e5b8a>)()
>       eval-last-sexp(nil)
>       funcall-interactively(eval-last-sexp nil)
>       command-execute(eval-last-sexp)

Adding João and Dmitry.