Fix for play issue (#1223)

See https://github.com/jambonz/jambonz-feature-server/issues/1222

lib/utils/sticky-event-emitter.js

@@ -37,6 +37,10 @@ class StickyEventEmitter extends EventEmitter {
         this.onSuccess();
       }
       this._onceListeners.delete(event);
+      // return from here as the event listener is already called
+      // this is to avoid calling the native emit method which
+      // will call the event listener again
+      return true;
     }
 
     return super.emit(event, ...args);