read_excel crash with empty Exception
If read one empty column from excel file, read_excel raise Exception without error message.
Small test case: content of excel file:

| A | B | C | D |
| --- | --- | --- | --- |
|  | 1 | 100 | f |
|  | 2 | 200 | f |
|  | 3 | 300 | f |
|  | 4 | 400 | f |

Run:

```
import pandas as pd
pd.read_excel("test_excel_.xls", parse_cols=[0], header=None)
```

Result:

```
File "/home/.../python2.7/site-packages/pandas/io/excel.py", line 170, in read_excelskip_footer=skip_footer, converters=converters, **kwds)
File "/home/.../python2.7/site-packages/pandas/io/excel.py", line 436, in _parse_excel**kwds)
File "/home/.../python2.7/site-packages/pandas/io/parsers.py", line 1346, in TextParserreturn TextFileReader(*args, **kwds)
File "/home/.../python2.7/site-packages/pandas/io/parsers.py", line 590, in __init__self._make_engine(self.engine)
File "/home/.../python2.7/site-packages/pandas/io/parsers.py", line 737, in _make_engineself._engine = klass(self.f, **self.options)
File "/home/.../python2.7/site-packages/pandas/io/parsers.py", line 1452, in __init__self.columns, self.num_original_columns = self._infer_columns()
File "/home/.../python2.7/site-packages/pandas/io/parsers.py", line 1735, in _infer_columnsline = self._buffered_line()
File "/home/.../python2.7/site-packages/pandas/io/parsers.py", line 1793, in _buffered_linereturn self._next_line()
File "/home/.../python2.7/site-packages/pandas/io/parsers.py", line 1817, in _next_lineraise StopIteration
```

Python 2.7.7
pandas 0.17.1
xlrd 0.9.4
