LruCacheObjectPersister’s getCreationDateInCache() does not ask fallback for date

I was using a LruCacheObjectPersister that decorated an InFileObjectPersister (fallback). When calling getCreationDateInCache(), LruCacheObjectPersister threw an exception about not finding the data although I could see that the cached file was existing. I expected LruCacheObjectPersister to return the last-modified of that cache file on disk.
Here's a patch + test to fix this.