Errors thrown in an Async#map don't always become Rejected

**Describe the bug**
If an error is thrown in an `Async#map`, it doesn't always become a `Rejected`.

**To Reproduce**
```js
const { Async } = require('crocks')

Async((rej, res) => res('a'))
.map(() => { throw new Error('bad') })
.fork(err => console.error({ err }), val => console.log({ val }))
```

**Expected behavior**
I would expect an object shaped like `{ err }` to be logged to `console.error`, but instead the error is thrown and logged by itself, and neither of the forked functions are called.

**Additional context**
If you wrap a Promise instead, it works as expected:
```js
Async.fromPromise(() => Promise.resolve('a'))('b')
.map(() => { throw new Error('bad') })
.fork(err => console.error({ err }), val => console.log({ val }))
```