ncrypt/crypt.c: Read the protected Message-ID

[alejandro-colomar]

I've seen some messages sent with thunderbird(1) which protected the Message-ID field. Let's read it if it's there.

Tested with an old mail I had in my mailbox:

...

[-- Begin signature information --]
Good signature from: Alejandro Colomar <alx@alejandro-colomar.es>
                aka: Alejandro Colomar <alx@kernel.org>
                aka: Alejandro Colomar Andres <alx.manpages@gmail.com>
            created: Thu Dec 22 15:11:26 2022
[-- End signature information --]

[-- The following data is signed --]
From: Alejandro Colomar <alx.manpages@gmail.com>
To: Deri <deri@chuzzlewit.myzen.co.uk>
Subject: Re: The Linux Manpages Book - Happy Christmas
Message-ID: <e5567e8b-def9-288a-c0bb-32ab3d67e3ea@gmail.com>
References: <1842694.tdWV9SEqCh@pip>
In-Reply-To: <1842694.tdWV9SEqCh@pip>

[-- Attachment #1 --]
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...

[alejandro-colomar]

BTW, I tried protecting this field in the past, but it's non-trivial, since it's not yet generated at the time we protect the fields, IIRC.