Bug in sample_by="paragraph"
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Thanks for reporting, @adampauls.

We are having a look at it. 
2022-12-01T07:58:46Z
https://github.com/huggingface/datasets/issues/5316#issuecomment-1333351153
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### Describe the bug

I think [this line](https://github.com/huggingface/datasets/blob/main/src/datasets/packaged_modules/text/text.py#L96) is wrong and should be `batch = f.read(self.config.chunksize)`. Otherwise it will never terminate because even when `f` is finished reading, `batch` will still be truthy from the last iteration.

### Steps to reproduce the bug

```
> cat test.txt
a b c

d e f
````

```python
>>> import datasets
>>> datasets.load_dataset("text", data_files={"train":"test.txt"}, sample_by="paragraph")
```

This will go on forever.

### Expected behavior

Terminates very quickly. 

### Environment info

`version = "2.6.1"` but I think the bug is still there on main. 