Fix typo + authentication-failure on empty attributes-array

An empty array shouldn't lead to an aborted logon.
Example when we try to get the 'mail' attribute:
UserA has a value set in the mail-attribute and passes the test -> Negotiate logon succeeds
UserB has an empty mail-attribute and fails the test -> Negotiate logon fails and the user has to log on manually (fallback to LDAP is initiated)