[BUG] org-num-skip-unnumbered is not respected if a org-mode file enables org-num-mode on startup [9.6.18 ( @ /home/drcxd/.emacs.d/elpa/org-9.6.18/)]

[Chang Xiaoduan <drcxd@sina.com>]

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Hello,

I have been experimenting with org-num-mode recently. I find that if an
org-mode file enables org-num-mode on startup by adding:

```emacs-lisp
#+STARTUP: num
```

and if there is a file local prop line:

```emacs-lisp
# -*- org-num-skip-unnumbered: t; -*-
```

then org-num-mode does not respect the file local variable, i.e., some
headings with the `UNNUMBERED` property set to `t` still get their
numbering. This also happens for `org-num-max-level` if it is set on the
file local prop line. If I toggle org-num-mode after visiting the
file, then org-num-mode respect those file local variables.

What's more, I have tried to remove the `STARTUP` keyword, so I can
enable org-num-mode after visiting the file. However, without enabling
org-num-mode on visiting the file, Emacs reports those file local
variables as unsafe, though their values are safe, according to the
documentation. I guess it is determined as unsafe because org-num-mode
is not loaded.

This can be reproduced by launching Emacs using `emacs -Q` and visiting
the following org-mode file:

```
# -*- org-num-skip-unnumbered: t; -*-

#+STARTUP: num

* Unnumbered Heading
:PROPERTIES:
:UNNUMBERED: t
:END:

* Numbered Heading
```

I expect that if I enable org-num-mode using the `STARTUP` keyword, it
will respect file local properties specified on the file local prop
line. Alternatively, Emacs should not report those file local variables
as unsafe if the org-num-mode is not enabled on startup.

Thank you

Xiaoduan

Emacs  : GNU Emacs 29.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.38, cairo version 1.16.0)
 of 2023-08-30, modified by Debian
Package: Org mode version 9.6.18 ( @ /home/drcxd/.emacs.d/elpa/org-9.6.18/)