dns: set error to REFUSED when there are no answers

modules/commands/os_dns.cpp

@@ -940,7 +940,6 @@ class ModuleDNS : public Module
 			if (packet->answers.size() == answer_size)
 			{
 				Log(this) << "Error! There are no servers with any IPs of type " << q.type;
-				/* Send back an empty answer anyway */
 			}
 		}
 	}

modules/m_dns.cpp

@@ -854,6 +854,9 @@ class MyManager : public Manager, public Timer
 				}
 			}
 
+			if (packet->answers.empty() && packet->authorities.empty() && packet->additional.empty() && packet->error == ERROR_NONE)
+				packet->error = ERROR_REFUSED; // usually safe, won't cause an NXDOMAIN to get cached
+
 			s->Reply(packet);
 			return true;
 		}