Fix memory leak in dns_message_checksig() - SIG(0) sigs

Impact should be visible only in tests or tools because named never
uses view == NULL, which is a necessary condition to trigger this leak.

(cherry picked from commit 69256b3553)

lib/dns/message.c

@@ -3227,7 +3227,8 @@ dns_message_checksig(dns_message_t *msg, dns_view_t *view) {
 
 		dns_rdataset_init(&keyset);
 		if (view == NULL) {
-			return (DNS_R_KEYUNAUTHORIZED);
+			result = DNS_R_KEYUNAUTHORIZED;
+			goto freesig;
 		}
 		result = dns_view_simplefind(view, &sig.signer,
 					     dns_rdatatype_key /* SIG(0) */, 0,