lib/client: always populate prefix for incoming messages

lib/client.js

@@ -158,6 +158,14 @@ export default class Client extends EventTarget {
 		if (!msg.prefix) {
 			msg.prefix = this.serverPrefix;
 		}
+		// Some servers send e.g. NOTICE messages before RPL_WELCOME
+		if (!msg.prefix) {
+			msg.prefix = {
+				name: null,
+				user: null,
+				host: null,
+			};
+		}
 
 		var msgBatch = null;
 		if (msg.tags["batch"]) {