Fix server error for UK domain

[ryankoga]

https://dzdb.caida.org/domains/UK causes a 500 server error, probably due to a lack of results in the database. If you search on https://dzdb.caida.org/search for UK (any record type), a link for UK domain appears (showing that it is recognized somewhere in the database) but clicking on that link returns the 500.

At the least, the lookup should recognize when no records are returned instead of causing a server error.