Improve appearance of MediaBBCode `[wsm]` for files without preview

[BurntimeX]

For media that are not image, video, or audio files, only a simple link is currently displayed.

ref https://www.woltlab.com/community/thread/296741-%C3%BCberarbeitung-des-mediabbcode-wsm-f%C3%BCr-dateien-ohne-vorschau/