Bug in masked array indexing.

This simple indexing operation

```
ma = np.ma.zeros(5000, dtype=[('symbol', 'O')])
print(ma[0])
```

fails with a

```
ValueError: Setting void-array with object members using buffer.
```

exception. While the non-masked version just works:

```
arr = np.zeros(5000, dtype=[('symbol', 'O')])
print(arr[0])
```

Numpy version `1.11.0` on python 3.5.1 on arch linux.
