bug#72329: Avoid recursion in gnus-message-citation-mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Thuna <thuna.cing@gmail.com>
> Date: Sun, 28 Jul 2024 03:30:40 +0200
> 
> In `gnus-message-citation-mode' the
> 
>   (if (not font-lock-mode)
>       (gnus-message-citation-mode (font-lock-mode 1))
>     ...)
> 
> can lead to excessive nesting if font-lock-mode fails to be set (quick
> enough or altogether).  Changing this with
> 
>   (while (not font-lock-mode) (font-lock-mode 1))
>   ...
> 
> should be better, assuming it is necessary for `font-lock-mode' to be
> called repeatedly, otherwise
> 
>   (font-lock-mode 1)
>   (while (not font-lock-mode))
>   ...
> 
> might also work, or simply
> 
>   (font-lock-mode 1)
>   ...
> 
> if it is not necessary to wait.
> 
> One possible problem with these arrangements is that it may be desirable
> to error in case there is an issue which prevents font-lock-mode from
> being set perpetually, in which case something like
> 
>   (font-lock-mode 1)
>   (with-timeout (<however-long-before-giving-up>
>                  (error "Failed to enable `font-lock-mode'."))
>     (while (not font-lock-mode)))
>   ...
> 
> might be preferable.

Thanks.

Eric, any comments or suggestions?