[BIDI] enterBr change direction in one line out of multiple

[garry.yao]

With "config.enterMode = CKEDITOR.ENTER_BR":

1. Load the following content and selection:

   <p>
   line1<br />
   line2^
   </p>
   

2. Click on 'RTL' button;
   • Actual Result: Affects the entire paragraph;
   • Expected Result: Second line that breaks away from the paragraph is only affected.

[tobiasz.cudnik]

Regression of [5977].

[Saare]

Fixed by Tobiasz with [6276].