Execa function may not pass stdout in callback function if run it with the `{ stdio: 'inherit' }` options.
Execa function may not pass stdout in callback function if run it with the `{ stdio: 'inherit' }` options.

Added a check for the presence of stdout in the object passed to the execa callback function.

fent/node-youtube-dl,przemyslawpluta/node-youtube-dl