go-resolver vulnerable to attacker-controlled domains due to unvalidated RRSIG RRs

go-resolver's DNSSEC validation is not performed correctly. An attacker can cause this package to report successful validation for invalid, attacker-controlled records. The owner name of RRSIG RRs is not validated, permitting an attacker to present the RRSIG for an attacker-controlled domain in a response for any other domain.