If PASS command is given (after unsuccessful USER) with plaintext auth disabled, give proper error message instead of "No username given".
If PASS command is given (after unsuccessful USER) with plaintext auth
disabled, give proper error message instead of "No username given".

--HG--
branch : HEAD

jwm/dovecot-notmuch,jkerihuel/dovecot,jwm/dovecot-notmuch,dscho/dovecot,jkerihuel/dovecot,jkerihuel/dovecot,dscho/dovecot,jwm/dovecot-notmuch,dscho/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot