Should not compress the root

Apparently, Knot 2 compress even the root. It is useless (since it is a zero-length label, only one byte) and, while legal, breaks some tools (see this bug report for Go DNS https://github.com/miekg/dns/issues/234#issuecomment-125299084 )

Knot 1.6 did not do that (you can test today on k-root)