AbstractResourceContainer logs warnings on 404

When an existing folder (but not a valid resource) is requested through the BinariesServlet, a RepositoryException is thrown and a warning is logged. For example: http://mysite.com/binaries/content/assets. For a 404 situation such as this, a warning in the logs is unexpected and unnecessary.

I've attached a patch that adds some extra checks to prevents the RepositoryException from being needlessly thrown, so no warnings are logged when a 404 occurs.