BUG: After reindex(),  astype() raises exception for categorical series
Hi 

I meet an unexpected behavior for  categorical series

After reindex() a categorical series, astype() will raise Exception

For example, code below raise ValueError: Wrong number of dimensions

```python
s = Series([1, 2, 3], index = [2, 0, 1])
(s.astype('category')
 .reindex([0, 1, 2])
 .astype(str))

```
However, if I reindex() first then set the series categorical, astype() works as expected.
Code below works fine

```python
s = Series([1, 2, 3], index = [2, 0, 1])
(s.reindex([0, 1, 2])
 .astype('category')
 .astype(str))
```

I think both code should behave the same way

