protectedSource is removed when it is the only source

[Patrick]

If a tag matches an item in the protectedSource regular expression and it is the only content, then it is removed when switching to WYSIWYG mode and back to Source mode.

Steps to reproduce:

1. Create a CKEditor using the following configuration:

   var config = {
                   protectedSource: [/<photo[0-9]+>/gi],
                   startupMode: 'source'
               };
   

2. Enter the text <photo1> into CKEditor.
3. Click the "Source" button to switch to WYSIWYG mode and click "Source" again to switch back to source mode

Expected Result:

1. CKEditor contains the content <photo1>

Actual Result:

1. CKEditor content is empty

[Jakub Ś]

Reproducible from CKEditor 3.0.2 in IE, Webkit and FF (4 and 5).

Works fine in FF 3.6.20 and Opera