Fix object not found exception when accessing to a proxy with CMIS

An error is displayed when viewing a proxy

Steps to reproduce

1. Add the following line in nuxeo.conf to enable proxy usage in CMIS

   org.nuxeo.cmis.proxies=true

2. As an administrator, create a user named cmis-user
3. Grant Read permission to cmis-user on the root of the repository
4. Deny Read permission to cmis-user on the root of the workspaces, or block the right inheritance
5. Create a section under the root of sections
6. Create a document and publish it to the newly created section. The document is now in version 1.0
7. As cmis-user, open CMIS Workbench and connect with cmis-user credentials to http://localhost:8080/nuxeo/json/cmis (Browser binding)
8. Browse the repository to the previously published document in the sections

A popup is displayed, with the error "ObjectNotFound" and the id of version which the proxy is based on.

No stacktrace in Nuxeo logs