Error reading an empty CSV with known column names and dtype 'category'
Hello, I've found a corner case where specifying `category` dtypes in `pd.read_csv` causes an error when it ought to return an empty dataframe.

#### A small, complete example of the issue

```python
pd.read_csv(StringIO(''), names=['a'], dtype={'a': 'object'}) #works

pd.read_csv(StringIO(''), names=['a'], dtype={'a': 'category'}) #breaks
```

#### Expected Output
```
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
/Users/dspitz/miniconda3/lib/python3.5/site-packages/pandas/io/parsers.py in read(self, nrows)
   1506         try:
-> 1507             data = self._reader.read(nrows)
   1508         except StopIteration:

pandas/parser.pyx in pandas.parser.TextReader.read (pandas/parser.c:10364)()

pandas/parser.pyx in pandas.parser.TextReader._read_low_memory (pandas/parser.c:11033)()

StopIteration: 

During handling of the above exception, another exception occurred:

TypeError                                 Traceback (most recent call last)
<ipython-input-13-819a0c4e04cb> in <module>()
----> 1 pd.read_csv(StringIO(''), header=None, names=['a'], dtype={'a': 'category'})

/Users/dspitz/miniconda3/lib/python3.5/site-packages/pandas/io/parsers.py in parser_f(filepath_or_buffer, sep, delimiter, header, names, index_col, usecols, squeeze, prefix, mangle_dupe_cols, dtype, engine, converters, true_values, false_values, skipinitialspace, skiprows, nrows, na_values, keep_default_na, na_filter, verbose, skip_blank_lines, parse_dates, infer_datetime_format, keep_date_col, date_parser, dayfirst, iterator, chunksize, compression, thousands, decimal, lineterminator, quotechar, quoting, escapechar, comment, encoding, dialect, tupleize_cols, error_bad_lines, warn_bad_lines, skipfooter, skip_footer, doublequote, delim_whitespace, as_recarray, compact_ints, use_unsigned, low_memory, buffer_lines, memory_map, float_precision)
    643                     skip_blank_lines=skip_blank_lines)
    644 
--> 645         return _read(filepath_or_buffer, kwds)
    646 
    647     parser_f.__name__ = name

/Users/dspitz/miniconda3/lib/python3.5/site-packages/pandas/io/parsers.py in _read(filepath_or_buffer, kwds)
    398         return parser
    399 
--> 400     data = parser.read()
    401     parser.close()
    402     return data

/Users/dspitz/miniconda3/lib/python3.5/site-packages/pandas/io/parsers.py in read(self, nrows)
    936                 raise ValueError('skipfooter not supported for iteration')
    937 
--> 938         ret = self._engine.read(nrows)
    939 
    940         if self.options.get('as_recarray'):

/Users/dspitz/miniconda3/lib/python3.5/site-packages/pandas/io/parsers.py in read(self, nrows)
   1513                 index, columns, col_dict = _get_empty_meta(
   1514                     names, self.index_col, self.index_names,
-> 1515                     dtype=self.kwds.get('dtype'))
   1516 
   1517                 if self.usecols is not None:

/Users/dspitz/miniconda3/lib/python3.5/site-packages/pandas/io/parsers.py in _get_empty_meta(columns, index_col, index_names, dtype)
   2803     col_dict = dict((col_name,
   2804                      np.empty(0, dtype=dtype.get(col_name, np.object)))
-> 2805                     for col_name in columns)
   2806 
   2807     return index, columns, col_dict

/Users/dspitz/miniconda3/lib/python3.5/site-packages/pandas/io/parsers.py in <genexpr>(.0)
   2803     col_dict = dict((col_name,
   2804                      np.empty(0, dtype=dtype.get(col_name, np.object)))
-> 2805                     for col_name in columns)
   2806 
   2807     return index, columns, col_dict

TypeError: data type "category" not understood
```

Appears the problem is in `_get_empty_meta()` where the `category` dtype is passed along to `np.empty`. I don't know the idiomatic way to construct an empty Categorical series but that is what needs to happen.

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

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Darwin
OS-release: 15.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.1
nose: None
pip: 8.1.1
setuptools: 20.3
Cython: 0.24.1
numpy: 1.11.2
scipy: 0.18.1
statsmodels: None
xarray: None
IPython: 5.1.0
sphinx: None
patsy: None
dateutil: 2.5.3
pytz: 2016.3
blosc: None
bottleneck: None
tables: 3.2.2
numexpr: 2.6.1
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.12
pymysql: 0.6.7.None
psycopg2: 2.6.1 (dt dec pq3 ext)
jinja2: 2.8
boto: None
pandas_datareader: None
</details>
