show name as @x if alias is set but topic is not

- e.g. @1 denotes alias 1 is set but topic is empty

packages/node_modules/@node-red/nodes/core/network/10-mqtt.html

@@ -275,7 +275,7 @@
         icon: "bridge.svg",
         align: "right",
         label: function() {
-            return this.name||this.topic||"mqtt";
+            return this.name||this.topic||(this.topicAlias ? "@"+this.topicAlias : "mqtt");
         },
         oneditprepare: function() {
             $("#node-input-broker").change(function(d){