Misuse of resolve/reject causes "close of closed channel" panic

Hello, 

If I run:

```go
mo.NewFuture(func(resolve func(struct{}), reject func(error)) {
	resolve(struct{}{})
	reject(errors.New("oh no..."))
})
```

I get `panic: close of closed channel`.

This makes me write defensive code (e.g. return after each call to reject / resolve).
I would suggest to recover from panics and reflect it as an error as part of `Result[T]`'s error.