Make it clear when IP address is not in the database

[chuwy]

scala-maxmind-iplookups uses Option[Either[Throwable, Result]] where Option represents a possible absence of a database file and Either[Throwable, _] represents both "invalid IP address passed" (like in snowplow/snowplow#4246) and "no such IP address in database".

It needs to clarify that IP address is not found.

Maybe should be implemented with #78