Infinite loop if action passed to every returns false

The [following line](https://github.com/davetemplin/async-parallel/blob/master/index.ts#L70) will cause an infinite loop if the action passed to every returns false.
```
return !result || list.length > 0;
```
As `!result` will be true even when the list is exhausted `true` will be passed to the pool indicating that is should keep looping.