allow mail with no subject to service desk

What does this MR do and why?

This allows emails to service desk without a subject. Many times customers miss adding a subject and the error message when this is rejected is not very helpful. So this is really bad for people trying to reach support but unable to get through without understanding why.

We have been using a work around to add '(no subject)' as subject using mailman to do this, but that complicates dmarc verification.

This patch was created by my colleague Jonathon Hall, I'm forwarding this on his behalf.

References

#330309

Screenshots or screen recordings

Before	After
Emails with empty subject rejected	Emails with empty subject accepted

How to set up and validate locally

1. Setup a service desk
2. Send an email with empty subject to the service desk
3. Without this patch, the email will be rejected, but with this patch it will be accepted.

MR acceptance checklist

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