Style info within <li> disappear after press Enter twice

[Satya Minnekanti]

To reproduce the defect

1. Open ajax sample.

2. Type four lines of data

3. Select all the text and click on Bullets and Center Justify Icons.

4. Go to HTML Source.you can find there is a style definition info within every list item

5. Go back to Rich Text and set the cursor on the last line,after item 4 & press Enter twice

Result:

The list is not at the center of the Editor, and at the left in fact.

Go to HTML Source, you will see that style definition info with each list item is lost.

[brooks]

and this bug happens in every samples,not just ajax examle.

[Garry Yao]

Please leave this ticket to me, it's rooted the same problem with #4950.

[Garry Yao]

Fixed by #4950.