When `domain_info` is passed an invalid domain, it would attempt to
parse the registered domain and eventually pass a blank string to
`pythonwhois.get_whois`. This causes an exception of "No root WHOIS
server found for TLD." This is a valid exception, but we should not make
it this far to get this exception.
Instead, this patch will raise an exception of `SatoriInvalidDomain` if
domain_info attempted to be used with an invalid domain.