Cannot edit pages relying on a sheet when user doesn't have edit rights

Reproduction steps:

• Install Repository server
• Create some extension pages with objects
• Create a user and forbid edit right
• Try to edit the extension page with change request

Expected result:

• The extension page should be entirely editable, like it is for a standard user

Obtained result:

• Only some part of the extension object are editable: main content appears to not be editable

Note: was tested directly on extensions.xwiki.org