fix: ws handle possible timeout

lib/websocket-client.js

@@ -62,7 +62,7 @@ module.exports = class WebsocketClient extends EventEmitter {
     this.logger.info('Closing connection', {category: 'bybit-ws'});
     this.readyState = READY_STATE_CLOSING;
     this._teardown();
-    this.ws.close();
+    this.ws && this.ws.close();
   }
 
   async _connect() {