Replace confusing empty 'Too many items.' page with Access Denied page

When the field cardinality is 1 and a user tries to add another field collection item then the message 'Too many items.' will be displayed and nothing else. A completely empty page otherwise, leaving the user confused.

Proposed solution: show the access denied page instead. Another field collection item cannot be added, so the appropriate response is to deny access. That is still not ideal for the end user, but at least the admin will see an access denied entry in the logs.