Ensure that a password exists after OTP validation
Before this patch users could log in using only the OTP value. This
arose because ipapwd_authentication() successfully determined that
an empty password was invalid, but 389 itself would see this as an
anonymous bind. An anonymous bind would never even get this far in
this code, so we simply deny requests with empty passwords.
This patch resolves CVE-2014-7828.
Reviewed-By: Alexander Bokovoy <firstname.lastname@example.org>