Fix EZP-22466: adv. obj. relation list edits not saved

Fixes the condition at the top of eZObjectRelationList::validateObjetAttributeHTTPInput().
It should now only skip validation if the attribute isn't required AND doesn't contain any relation.

The issue was a regression from https://jira.ez.no/browse/EZP-18790. The bug fixed in this issue
was tested, and no regression was found.
Revert "Fix EZP-22466: adv. obj. relation list edits not saved"

This reverts commit 74835762e8c7fcec3ccbd8d9d2c6ebcd69f9ec1b.
Replaced by 48426e9.
Merge branch 'EZP-22466-advanced_object_relation_list_editing-take_2'

Fixes embedded edition of content through the ezobjectrelationlist
datatype, by fixing a wrong condition in eZObjectRelationList::validateObjectAttributeHTTPInput(),
that was preventing the method from being executed correctly.