message: Raise ValueError when linspace is called with num == 0. Update docstring.
diff: @@ -109,12 +109,13 @@ nextafter = gen_math_ops.next_after
  def linspace_nd(start, stop, num, name=None, axis=0):
  r"""Generates evenly-spaced values in an interval along a given axis.
  - Matches [np.linspace](https://docs.scipy.org/doc/numpy/reference/generated/numpy.linspace.html)'s behaviour.
  - A sequence of `num` evenly-spaced values are generated beginning at `start`.
  + A sequence of `num` evenly-spaced values are generated beginning at `start`
  + along a given `axis`.
  If `num > 1`, the values in the sequence increase by `stop - start / num - 1`,
  - so that the last one is exactly `stop`.
  + so that the last one is exactly `stop`. If `num <= 0`, `ValueError` is raised.
  - When `num == 0`, returns a tensor with `0` elements along the given `axis`.
  + Matches [np.linspace](https://docs.scipy.org/doc/numpy/reference/generated/numpy.linspace.html)'s behaviour
  + except when `num == 0`.
  For example:
  @@ -178,7 +179,7 @@ def linspace_nd(start, stop, num, name=None, axis=0):
  delta = (expanded_stop - expanded_start) / n_steps
  # If num < 0, we will throw exception in the range
  # otherwise use the same div for delta
  - range_end = array_ops.where_v2(num_int >= 0, n_steps, -1)
  + range_end = array_ops.where_v2(num_int > 0, n_steps, -1)
  num_range = range(1., range_end, dtype=start.dtype)
  shape_range = range(ndims)
  ones_like_shape_range = array_ops.ones_like(shape_range)
  