Return no more than ``k`` indices of smallest values.

def argsort_k_smallest(x, k):
    """ Return no more than ``k`` indices of smallest values. """
    if k == 0:
        return np.array([], dtype=np.intp)
    if k is None or k >= len(x):
        return np.argsort(x)
    indices = np.argpartition(x, k)[:k]
    values = x[indices]
    return indices[np.argsort(values)]