[BUG] Empty DataFrame object columns property doesn't match pandas for data=None or data={}.

[wence-]

Describe the bug

When constructing an empty dataframe where one does not explicitly specify the column names, pandas produces a RangeIndex for the .columns property.

In contrast, cudf produces an Index(dtype=object) if data={} or data=None.

Steps/Code to reproduce bug

import cudf
import pandas as pd

for data in [{}, None]:
    columns = cudf.DataFrame(data=data).columns
    expect = pd.DataFrame(data=data).columns

    assert type(columns) == type(expect)

Expected behavior

Matching pandas. This works if data is an empty list-like object (e.g. data=[]) so it's probably just another condition to handle.