Do not filter version images if VERSIONS_BASEDIR is in use

If VERSIONS_BASEDIR is specified, there is no need to filter file list while browsing directory.
I use VERSIONS_BASEDIR to guarantee that user is unable to upload file incorrectly recognized as version file (and being hidden in browse view). Without this commit, user uploaded file "product_list_index.pdf" is hidden when there is "index" image VERSION.