Fix invalid email error in process_forms

[jeremydstone]

Since forever, we have occasionally had emails get submitted in forms that are later judged invalid by Poste. When Poste throws an exception about an invalid email, that completely stops our process_forms cron job and requires manual intervention to repair.

This PR makes process_forms more robust so the entire job does not fail due to a single invalid email address. process_forms now rescues from an "Invalid email address" exception from Poste and continues, marking the form as processed. (The same thing we do to repair manually.)

This problem (though infrequent) occurs because we have different (and less stringent) email validation rules in place elsewhere on the site. We should consider tracking these down and making Poste and the rest of our site use the same validation rules. This fix is worth having even if we align the email validation as well, since the present behavior of one invalid entry making the whole process fail is not robust.

[aoby]

Thanks for fixing!

Let's add the follow up to our tech debt tracking doc, so we don't lose track of it.

[jeremydstone]

Also: tested locally by running process_forms against some local data with valid and invalid emails set and made sure the changes behaved as expected.