Improve robustness.

lib/controller.js

@@ -113,6 +113,7 @@ class Controller {
         const deviceID = Object.keys(settings.get().devices).find((id) => settings.get().devices[id].friendly_name === friendlyName);
         if (!deviceID) {
             logger.error(`Cannot handle '${topic}' because deviceID of '${friendlyName}' cannot be found`);
+            return;
         }
 
         // Convert the MQTT message to a Zigbee message.