[O] Prevent auto-fill-mode from filling Property values in drawers

[Kaushal Modi]

Hello,

I have noticed that auto-filling working on long (going past fill-column) values in property drawers.

Here's a MWE:

=====
#+TITLE: Test case showing auto-filling happening in Property drawers too
* Heading
:PROPERTIES:
:DESCRIPTION: This is a very long description that will auto fill at the =fill-column=. But this is inside a property drawer, so the auto-filling should be disabled.
:END:
* COMMENT Local Variables
# Local Variables:
# fill-column: 70
# eval: (auto-fill-mode 1)
# End:
=====

The value of that DESCRIPTION property is in a single line (I believe some email clients auto-fill the text). Basically this is what it should look like in emacs -Q after M-x toggle-truncate-lines:

Now if you hit return at the end of that long description, auto-fill kicks in and turns that into this invalid drawer:

=====
#+TITLE: Test case showing auto-filling happening in Property drawers too
* Heading
:PROPERTIES:
:DESCRIPTION: This is a very long description that will auto fill at
the =fill-column=. But this is inside a property drawer, so the
auto-filling should be disabled.

:END:
* COMMENT Local Variables
# Local Variables:
# fill-column: 70
# eval: (auto-fill-mode 1)
# End:
=====

This looks like a bug. Can the auto-filling be disabled in property drawers?

I can recreate this issue on both:

- Org stable (9.1.6 that's on emacs-26 branch) :: Org version: Org mode version 9.1.6 (release_9.1.6-50-g96b33f @ /home/kmodi/usr_local/apps/6/emacs/emacs-26/share/emacs/26.0.91/lisp/org/)

- Org master ::Org mode version 9.1.6 (release_9.1.6-395-g8ecc4c @ /home/kmodi/usr_local/apps/6/emacs/emacs-26/share/emacs/site-lisp/org/)

Thanks.

--

Kaushal Modi