mail/dovecot,mail/dovecot-pigeonhole: fix CVE-2019-11500

Changes

• CVE-2019-11500: IMAP protocol parser does not properly handle NUL byte when scanning data in quoted strings, leading to out of bounds heap memory writes. Found by Nick Roessler and Rafi Rubin.

MFH: 2019Q3
Security: CVE-2019-11500