Main attachment preview does not work when document has the Folderish facet

1. create a document type named ComposedDocument extending File
2. in the forms add 2 widgets:
   • one for *file:content*
   • one for *file:files*
3. add the Folderish facet
4. save project
5. install nuxeo 8.10 or later
6. synchronize the project
7. create a document of type ComposedDocument
8. add the azeaze.xls file as main attachment and in the files section
9. save the document
10. try to preview the main attachment (eye icon)
11. observe it displays the following error:

    {"entity-type":"exception","status":404,"message":"Preview not available"}
    

12. try to export as pdf the main attachment (PDF icon) and observe it works fine
13. try to preview the second attached file and observe it works fine

Now remove the Folderish facet in the Studio project and replay the same scenario. Everything works fine.

There are no errors in the Nuxeo server logs.
Comparing the onclick javascript for folderish and non-folderish documents reveals they are the same.