not all results have 'dn'

On the local AD/LDAP system, authenticate(login, pass) produces a result list of length 4 and only the first item is the user info of interest, the other 3 look more or less like:

{'type': 'searchResRef', 'uri': ['ldaps://zone.some.lan/DC=zone,DC=some,DC=lan']}
{'type': 'searchResRef', 'uri': ['ldaps://otherzone.some.lan/DC=otherzone,DC=some,DC=lan']}
{'type': 'searchResRef', 'uri': ['ldaps://some.lan/CN=Configuration,DC=some,DC=lan']}

Patch fixes the "key error" issue for me.