Prevent Bluebird warning about a promise not being returned from a handler

[MattiasBuelens]

The polyfill often creates new promises within a fulfillment/rejection handler of a different promise, without returning that new promise. Bluebird thinks this might be a mistake, and logs a warning when this happens. However, in our case, these are not mistakes.

Reproducing this issue is surprisingly easy. Even basic usage of the polyfill is enough to trigger these warnings:

<script src="https://cdn.jsdelivr.net/bluebird/latest/bluebird.js"></script>
<script src="https://unpkg.com/web-streams-polyfill@3.1.1/dist/polyfill.min.js"></script>
<script>
const rs = new ReadableStream({
  start(c) {
    c.enqueue('a');
    c.enqueue('b');
    c.close();
  }
});
const ws = new WritableStream({
  write(chunk, c) {
    console.log(chunk);
  }
});
rs.pipeTo(ws);
</script>

Fix it by returning null from all problematic fulfillment/rejection handlers, to suppress these warnings.

Supersedes #90.

[Setitch]

Oh my, You were faster than me - (sat at that hour ago again and started adding returns----, but im glad You found it^^ I also see you added optimization of setting only one function for the variables at time without overriding them

[MattiasBuelens]

Oh my, You were faster than me - (sat at that hour ago again and started adding returns)

Yeah. Luckily we were already using helper functions for adding fulfillment/rejection handlers to promises, so I could change the type from void to null there and then find and fix all type errors. (I absolutely love static types for refactorings like these! 😁)

Since it's not that critical of a bug (I hope), I'm not going to make a separate patch release for it. Instead, it'll go into the 4.0 release, if that's okay with you.

[Setitch]

For now i hide the warnings, it will take A WHILE for this changes to be incorporated into openpgp library and then to project using it, so i really dont mind. Im happy thought we could improve the codebase^_^

[MattiasBuelens]

Released as v4.0.0-beta.2. 🚀