The resource picker is not reset before creating a new link

The resource picker text input should be empty when creating a new link, no matter what link type you choose. The following behaviour was reported by chkumar and is a consequence of this issue:

CKEditor link-dialog does not set the hyperlink in the highlighted text if the URL text-box in the link-dialog box already has a pre-filled URL from a previous link.

Steps to reproduce:
1. Create a hyperlink on any page. Say type 'foo', click link icon in CKEditor, select 'URL' from split button, enter http://xwiki.org. This will create the link perfectly. Verify the source of the link, it should be [[foo>>http://xwiki.org]\]
2. Now create a new hyperlink. Say type 'bar', click link icon in CKEditor, select 'URL' from split button, notice that http://xwiki.org is already pre-filled. Now don't change the link, simply select 'OK'. Now notice the source of the link - there's no link over there. It should look like this: [[bar>>]].

So, what I think happened is that the URL object needed to print the URL in the Wiki syntax did not get set because the URL did not change in the text-box.