Add dns_nsec_requiredtypespresent

checks an NSEC rdataset to ensure that both NSEC and RRSIG are
present in the type map.  These types are required for the NSEC
to be valid

lib/dns/resolver.c

@@ -5572,6 +5572,15 @@ answer_response:
 				continue;
 			}
 
+			/*
+			 * Don't cache NSEC if missing NSEC or RRSIG types.
+			 */
+			if (rdataset->type == dns_rdatatype_nsec &&
+			    !dns_nsec_requiredtypespresent(rdataset))
+			{
+				continue;
+			}
+
 			/*
 			 * Don't cache "white lies" but do cache
 			 * "black lies".