Too many EmptyCell's retrieved from ReadOnlyWorksheet
*Created originally on Bitbucket by [Pravin Kumar](https://bitbucket.org/%7Baba9ec5d-a8da-49e9-84e9-45c5fa48d136%7D/)*
One extra EmptyCell is retrieved when an empty range is selected. I'm not sure why any cells are retrieved at all, I thought an empty set should be returned. This only happens on the attached workbook, which is a stripped-down version of a production one I am working with. I created this workbook with Excel 2016.
Here is a minimal example, applied on the attached excel workbook:
```
#!python
import openpyxl
wb = openpyxl.load_workbook(filename='test_empty.xlsx', read_only=True)
ws = wb['Main']
# Should be length 2, but is length 3
ref = 'D2:E2'
print(ref)
print([x.value for x in ws[ref][0]])
print(len(ws[ref][0]))
# Should be length 5 and is length 5
ref2 = 'A2:E2'
print(ref2)
print([x.value for x in ws[ref2][0]])
print(len(ws[ref2][0]))
```
Outputs
```
#!python
D2:E2
[None, None, None]
3
A2:E2
['a', 'b', None, None, None]
5
```
openpyxl 2.4.8 (pip installation)
Python 3.6.2 (v3.6.2:5fd33b5, Jul 8 2017, 04:14:34) [MSC v.1900 32 bit (Intel)] on win32
Windows 10, Excel 2016
Screenshot of test_empty.xlsx:

Screenshot from my actual project, debugged in PyCharm:

I'm happy to have a go at fixing this bug, if you can give me an idea of where to start. Thanks
*Attachments:* [test_empty.xlsx](/uploads/4f1f6bd344b8fc0405f2511b34f97d62/test_empty.xlsx)
issue