Error Indexing DafaFrame with a 0-d array
```python
>>> df = pd.DataFrame([[1, 2], [3, 4]], columns=['a', 'b'])
>>> ar = np.array(0)
>>> df.iloc[ar]
Traceback (most recent call last):
  ...
  ...
  File "/home/float2/Documents/Python/Pandas/pandas/pandas/core/indexes/base.py", line 529, in _shallow_copy_with_infer
    if not len(values) and 'dtype' not in kwargs:
TypeError: object of type 'numpy.int64' has no len()

```
A 0-d array passes [this](https://github.com/pandas-dev/pandas/blob/1a23779f09abc6ebf908d66ee88b973b767e2e3c/pandas/core/indexing.py#L2090) check cause it is an Iterable. But later, when **len()** is called on, TypeError is raised.
It would be nice to implement [PEP 357](https://www.python.org/dev/peps/pep-0357/) to prevent this error.
The matter has been raised at PyTorch project. [#9237](https://github.com/pytorch/pytorch/pull/9237)