ldap authenticator problems

[Cantor, Scott]

The easiest way I managed to reproduce what I think is that exact error is by uncommenting but also clearing out the idp.authn.LDAP.authenticator property in ldap.properties

That's nothing I would expect anybody to accidentally do, but that does create the exception.

We can patch the NPE regardless so it's not just crashing that way, but the code has to have one of those authenticator "types" to wire things up with default behavior so it's got to be something, or left undefined so it defaults.

-- Scott