AD won't return an error if you bind with no password

For example

  var client = ldap.createClient({ url: 'ldap://ldap/', });

  client.bind('CN=user', '', function(err) {
    if(err){ console.log("ERROR"); }
    }
  });

doesn't print anything.

You will get an error at a search etc. But in this case we need to bail out
otherwise we allow users to authenticate with no password!
Merge pull request #3 from johnf/master

AD won't return an error if you bind with no password