Pandas.read_html missing converted data
pandas version:
 '0.19.2'
```python

import requests
url ="http://www.hkex.com.hk/chi/market/sec_tradinfo/stockcode/eisdeqty_c.htm"
response = requests.get(url)
if response.status_code == 200:
        soup = BeautifulSoup(response.content, "lxml")
        table = soup.find("table", class_="table_grey_border")
        board_data = pandas.read_html(table.prettify(),header=0, flavor="bs4")
        
        return board_data[0]


```
#### Problem description

```
       股份代號             股份名稱   買賣單位   附註 Unnamed: 4 Unnamed: 5 Unnamed: 6
0         1               長和    500    #          H          O          F
1         2             中電控股    500    #          H          O          F
2         3           香港中華煤氣   1000    #          H          O          F
3         4            九龍倉集團   1000    #          H          O          F
4         5             匯豐控股    400    #          H          O          F
5         6             電能實業    500    #          H          O          F
6         7             凱富能源   2000    #        NaN        NaN        NaN

```

股份代號 this column data should be `1->00001`, `2->00002`

datatype:
股份代號           int64
股份名稱          object
買賣單位           int64
附註            object
Unnamed: 4    object
Unnamed: 5    object
Unnamed: 6    object
dtype: object
<class 'pandas.core.frame.DataFrame'>



why missing the 0000 data in the columns

actually, the 股份代號 datatype should be object.

