The previews-finished push notification is ignored

The `Processing this file. Grab some tea and sit back.` screen doesn't go away and load the filepreview when a file has finished processing. The thumbnail does seem to change.

Steps to reproduce:

1. Upload a PDF file (something that takes a little while)
2. Go to the content profile
3. Wait a little bit
4. You should see the `previews-finished` notification come in over the websocket but the spinner-screen is still there