Compatibility with RFC 2181

According to RFC2181, every DNS query needs to have a . at the end of
the name record you are requesting.

This will show that that name record is the root of the domain you are
asking
In some cases, when the . is missing, the hostname of the server the
code is running on will be appended to the name record when
checkdnsrr() is being executed and this will in turn return a false
positive when there is a wildcard DNS record for the root domain of the
hostname of the server.