Fix for getting an Array item

Getting an Array by index will return the [idx:] instead.  Only occurs when carray.getitem_cache fails.

```python

import blaze as blz
import numpy as np
shape = (366,624,1406)
a = np.arange(366*624*1406).reshape(shape)
b = blz.Array(a,dshape=blz.dshape('366,624,1406 int32'))
assert b[0].shape == (624,1406)
```