TST: `read_csv` with chunksize set returns empty `DataFrame` Instead of `TextFileReader`
#### Code Sample

```python
import pandas as pd

# data.csv is an empty file
df = pd.read_csv('data.csv', chunksize=20, header=None, names=['a', 'b', 'c'])

```
#### Problem description
`read_csv` returns an empty DataFrame instead of a `pandas.io.parsers.TextFileReader` object when the above code is run. While this isn't a big issue, it is unexpected and the only way to tell the file is empty (through Pandas) is to check if a DataFrame was returned by `read_csv`. It would make more sense if `None` was returned instead, or the `TextFileReader`.

#### Expected Output
`pandas.io.parsers.TextFileReader` object 

#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-47-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.1
nose: None
pip: 9.0.1
setuptools: 25.1.1
Cython: None
numpy: 1.11.2
scipy: 0.18.1
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2016.7
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.3
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
pandas_datareader: None
</details>
