EssentialsListComponent should show no docs (not all site docs) if path is invalid

If the path configured for EssentialsListComponent does not point to an existing folder then the search scope used will be the site content base bean. This leads to unexpected behavior as rather than a null or empty list you get a list of all documents (assuming no type restrictions). This behavior is unexpected and makes it difficult if not impossible to guard against this condition. An invalid path should lead to a null search scope. This is distinct from an empty on missing path which behavior is documented and leads to a scope of the content bean. That is not the same case however as an explicit path implies a different intent than a missing path.