BUG: fix random.choice scalar object result and disallow 0-d arrays

Object arrays failed due to bad check for finding out if the result should
be a scalar type and not an array when size=None. Also in this case the
creation of the new array was wrong. This should be fixed with this.

The second fix is to forbid 0-d arrays. Allowing 0-d arrays does not
make much sense. But it is dangerous because for example floats will
be interpreted as 1-d arrays, while one may expect that they are interpreted
as integers. This also saves the trouble of reliably detecting all integers...