prevent callback to call twice

{ Error: Request Timeout after 30000ms
    at /usr/local/app/node_modules/elasticsearch/src/lib/transport.js:362:15
    at Timeout.<anonymous> (/usr/local/app/node_modules/elasticsearch/src/lib/transport.js:391:7)
    at ontimeout (timers.js:436:11)
    at tryOnTimeout (timers.js:300:5)
    at listOnTimeout (timers.js:263:5)
    at Timer.processTimers (timers.js:223:10)
  status: undefined,
  displayName: 'RequestTimeout',
  message: 'Request Timeout after 30000ms',
  body: undefined }
Error [ERR_MULTIPLE_CALLBACK]: Callback called multiple times
    at ElasticsearchTransformer.afterTransform (_stream_transform.js:85:31)
    at runCallback (timers.js:705:18)
    at tryOnImmediate (timers.js:676:5)
    at processImmediate (timers.js:658:5)