Nameserver identification fix

©! I, Hugo Landau <hlandau@devever.net>, hereby licence these changes under the
©! licence with SHA256 hash
©! fd80a26fbb3f644af1fa994134446702932968519797227e07a1368dea80f0bc.

server/server.go

@@ -78,10 +78,12 @@ func New(cfg *Config) (s *Server, err error) {
 		},
 	}
 
+	if s.cfg.CanonicalNameservers != "" {
 		s.cfg.canonicalNameservers = strings.Split(s.cfg.CanonicalNameservers, ",")
 		for i := range s.cfg.canonicalNameservers {
 			s.cfg.canonicalNameservers[i] = dns.Fqdn(s.cfg.canonicalNameservers[i])
 		}
+	}
 
 	if s.cfg.VanityIPs != "" {
 		vanityIPs := strings.Split(s.cfg.VanityIPs, ",")