Promise.reject() without an arg should be treated as a Promise rejection

[ZacharyRSmith]

Do you want to request a feature or report a bug?

bug

What is the current behavior?

eachAsync does not recognize fn calling reject() without an arg as a Promise rejection.

If the current behavior is a bug, please provide the steps to reproduce.

const cursor = Model.find({}).cursor();
const fn = new Promise((resolve, reject) => reject());
cursor.eachAsync(fn, err => {
  console.log('err', err); // undefined
});

What is the expected behavior?

Calling reject() should be treated as a Promise rejection.

Please mention your node.js, mongoose and MongoDB version.

node.js: >=6.11.4
mongoose: 4.13.7-pre
MongoDB: 3.2.7

[vkarpov15]

Fixed by #5875