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