BUG: Converters handling inconsistent with usecols
use attached file and run script
[csv2.txt](https://github.com/pandas-dev/pandas/files/1514678/csv2.txt)

```python
import re
from pandas import read_csv

kw = {'engine': 'python', 'header': 0, 'usecols': [2, 1], 'iterator': True}
kw['sep'] = "[" + re.escape("\t,") + "]" # or just "\t,"
kw["converters"] = {i: lambda(value): value for i in kw["usecols"]} # if comment this line or set 'usecols' : [0, 1] or 'sep': ","   -  work good
reader = read_csv("path to attached csv2.txt file", **kw)
print "rows", [row for row in reader.get_chunk().values]

```
#### Problem description
```
  print "rows", [row for row in reader.get_chunk().values]
  File "/tmp/opt/linux-CentOS_4.4-x64/P7/python-2.7.7-dbg/lib/python2.7/site-packages/pandas/io/parsers.py", line 768, in get_chunk
    return self.read(nrows=size)
  File "/tmp/opt/linux-CentOS_4.4-x64/P7/python-2.7.7-dbg/lib/python2.7/site-packages/pandas/io/parsers.py", line 747, in read
    ret = self._engine.read(nrows)
  File "/tmp/opt/linux-CentOS_4.4-x64/P7/python-2.7.7-dbg/lib/python2.7/site-packages/pandas/io/parsers.py", line 1610, in read
    data = self._convert_data(data)
  File "/tmp/opt/linux-CentOS_4.4-x64/P7/python-2.7.7-dbg/lib/python2.7/site-packages/pandas/io/parsers.py", line 1643, in _convert_data
    col = self.orig_names[col]
IndexError: list index out of range
```



<details>

Terminal INSTALLED VERSIONS
Terminal ------------------
Terminal commit: None
Terminal python: 2.7.7.final.0
Terminal python-bits: 64
Terminal OS: Linux
Terminal OS-release: 4.4.0-97-generic
Terminal machine: x86_64
Terminal processor: x86_64
Terminal byteorder: little
Terminal LC_ALL: None
Terminal LANG: en_US.UTF-8
Terminal LOCALE: en_US.UTF-8
Terminal 
Terminal pandas: 0.20.1
Terminal pytest: None
Terminal pip: 9.0.1
Terminal setuptools: 1.1.6
Terminal Cython: None
Terminal numpy: 1.11.2
Terminal scipy: 0.18.1
Terminal xarray: None
Terminal IPython: 0.13.2
Terminal sphinx: None
Terminal patsy: None
Terminal dateutil: 2.3
Terminal pytz: 2014.10
Terminal blosc: None
Terminal bottleneck: None
Terminal tables: None
Terminal numexpr: None
Terminal feather: None
Terminal matplotlib: 1.5.0
Terminal openpyxl: 2.3.0
Terminal xlrd: 0.9.4
Terminal xlwt: 1.0.0
Terminal xlsxwriter: None
Terminal lxml: None
Terminal bs4: None
Terminal html5lib: None
Terminal sqlalchemy: None
Terminal pymysql: None
Terminal psycopg2: None
Terminal jinja2: 2.8
Terminal s3fs: None
Terminal pandas_gbq: None
Terminal pandas_datareader: None

</details>
