Lps 50298

This is a fix for documents and media so that the correct documents and media list appears in staging. 

Currently, there is a bug for staging and web content structures that occur if these conditions are present:
- a site is staged, but the documents and media portlet is not staged for the site
- a structure is created with a documents and media field
- when creating a web content article using that structure, no documents will be returned by the documents and media field

I added a check in the document selector so that the correct group id is used when the documents and media portlet is not staged.