BUG: np.ma.where does not handle structured dtypes correctly #8600

>>> dt = np.dtype([('a', int), ('b', int)])
>>> x = np.array([(1, 2), (3, 4)], dtype=dt)
>>> np.where([0, 1], x, np.array((2, 3), dtype=dt)).dtype
dtype([('a', '<i4'), ('b', '<i4')])
>>> np.ma.where([0, 1], x, np.array((2, 3), dtype=dt)).dtype
dtype('O')