Make nuxeo-document-suggestion handle non visible and deleted documents

Steps to reproduce

1. Deploy the attached jar to nxserver/plugins
2. Go to a Workspace or to the Admin workspace
3. Create a Document "Suggest Doc" and select 3 documents for the "docus" field: Templates, Workspaces and Sections
4. Go to the Domain and delete the Sections document. Then empty the trash
5. Go back to the newly created document
6. Observe that nothing is displayed for the "docus" field
7. Edit the document
8. Observe that nothing is displayed in the suggestion field for "docus"

Expected behavior:

At least, the suggestion field should display the values which correspond to non -deleted documents. Note that a similar problem may happen if the current user cannot read one of the target documents.

A better solution would be to display a little icon to inform that the target document has been deleted or is not accessible (permission restriction) if it's possible to make this distinction.