SNMPv3Enum misses users where there's no authentication

[raesene]

If a response comes back to a user enumeration request where it allows the request just with the username, the enum script barfs as it's not one of our two handled cases.

Need to add a third case, likely where it matches the OID requested.

iso.3.6.1.2.1.1.1.0

would seem like a plausible string to match.