uni_ucs4_to_utf8(): Check len>0 first so we don't access input[len].
uni_ucs4_to_utf8(): Check len>0 first so we don't access input[len].

--HG--
branch : HEAD

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