Logic bug in arrow_writer?
https://github.com/huggingface/datasets/blob/88a902d6474fae8d793542d57a4f3b0d187f3c5b/src/datasets/arrow_writer.py#L475-L488

I got some error, and I found it's caused by `batch_examples` being `{}`. I wonder if the code should be as follows:
```
-        if batch_examples and len(next(iter(batch_examples.values()))) == 0:
+       if not batch_examples or len(next(iter(batch_examples.values()))) == 0:
            return
```
@lhoestq 