SECURITY UPDATE: imap-login excessive memory usage DoS (ELSCVE-123445)
debian/patches/CVE-2026-27857.patch: limit IMAP parser open list
count via new imapparserparams struct; cap pre-auth
IMAPLOGINLISTCOUNTLIMIT to 1. Squashes upstream commits
825bc297, d0f67b52, af1fb4da, 3435e0d44.