Type error when calling `map` over dataset containing 0-d tensors
### Describe the bug

0-dimensional tensors in a dataset lead to `TypeError: iteration over a 0-d array` when calling `map`.  It is easy to generate such tensors by using `.with_format("...")` on the whole dataset.

### Steps to reproduce the bug

```
ds = datasets.Dataset.from_list([{"a": 1}, {"a": 1}]).with_format("torch")
ds.map(None)
```

### Expected behavior

Getting back `ds` without errors.

### Environment info

Python 3.10.8
datasets 2.6.
torch 1.13.0