read_fwf - parsers.py PythonParser._rows_to_columns line 2814 object of type 'NoneType' has no len()
Line 2814 in parsers.py throws an error if self.delimiter is None:

"object of type 'NoneType' has no len()"

Here is the current line of code where the error happens:

```python
if len(self.delimiter) > 1 and self.quoting != csv.QUOTE_NONE:
    # see gh-13374
    reason = ('Error could possibly be due to quotes being '
        'ignored when a multi-char delimiter is used.')
    msg += '. ' + reason
```

I propose the following fix, which I believe should be a safe replacement:

```python
if self.delimiter is not None and len(self.delimiter) > 1 and self.quoting != csv.QUOTE_NONE:
```

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.4.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 158 Stepping 9, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None
pandas: 0.20.3
pytest: 3.2.1
pip: 9.0.1
setuptools: 36.5.0.post20170921
Cython: 0.26.1
numpy: 1.13.1
scipy: 0.19.1
xarray: None
IPython: 6.1.0
sphinx: 1.6.3
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.2
feather: None
matplotlib: 2.0.2
openpyxl: 2.4.8
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 0.9.8
lxml: 3.8.0
bs4: 4.6.0
html5lib: 0.999999999
sqlalchemy: 1.1.13
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: None

</details>
