Always consult CacheLoader if entry is not in data container

Currently we do not query the underlying persistence layer when an entry was found to be expired in memory. However it makes sense to query a CacheLoader (that is that it doesn't implement CacheStore) even when an entry is expired. This allows for users to configure a CacheLoader that always returns non null and the cache will never return null.

Please see https://github.com/infinispan/infinispan/pull/6071 more information