Forward plugin: if we got nothing but errors, return the last response we got

fixes #2882

Author: jedisct1

dnscrypt-proxy/plugin_forward.go

@@ -322,19 +322,19 @@ func (plugin *PluginForward) Eval(pluginsState *PluginsState, msg *dns.Msg) erro
 				continue
 			}
 		}
-		if len(sequence) > 0 {
-			switch respMsg.Rcode {
-			case dns.RcodeNameError, dns.RcodeRefused, dns.RcodeNotAuth:
-				continue
-			}
-		}
 		if edns0 := respMsg.IsEdns0(); edns0 == nil || !edns0.Do() {
 			respMsg.AuthenticatedData = false
 		}
 		respMsg.Id = msg.Id
 		pluginsState.synthResponse = respMsg
 		pluginsState.action = PluginsActionSynth
 		pluginsState.returnCode = PluginsReturnCodeForward
+		if len(sequence) > 0 {
+			switch respMsg.Rcode {
+			case dns.RcodeNameError, dns.RcodeRefused, dns.RcodeNotAuth:
+				continue
+			}
+		}
 		return nil
 	}
 	return err