Geary.Imap.Quirks: Add quirks for Dovecot

Dovecot 2.3.4.1 and earlier uses "MISSING_MAILBOX" and "MISSING_DOMAIN"
in the address structures of FETCH ENVELOPE replies when the mailbox or
domain is missing.

See https://dovecot.org/pipermail/dovecot/2020-August/119658.html
3 jobs for mjog/dovecot-envelope-mailbox-quirk in 32 minutes and 56 seconds (queued for 1 second)