v6.1.1 hangs when stdin is discarded

With v6.1.1, this no longer exits:

```js
import ora from 'ora'
const spinner = ora('test').start()
setTimeout(() => spinner.succeed(), 1000)
```

Changing the arg to `{ text: 'test', discardStdin: false }` fixes it, which makes sense, as #210 introduced a change to the code that handles stdin.

I'm observing this on Node v14, v16, and v18.