Still some layout jumps with rich workspaces

[juliusknorr]

@juliushaertl layout jumps does not occur on first page load, however, if you refresh the page or open and close an image from the viewer, layout jump still occurs.

Originally posted by @maximelehericy in #4776 (comment)

Sometimes the preview text from the webdav response does not seem to get rendered fully, to be investigated further