If blocking userdb lookup fails, don't crash. Also we shouldn't stop trying other userdbs then.
If blocking userdb lookup fails, don't crash. Also we shouldn't stop trying
other userdbs then.

--HG--
branch : HEAD

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