if I upload a file using the server file uploader, the notebook file API is not aware

This case happens if a user uploads a file using the revisions page while the notebook associated with that file is also open. The redux store on the client doesn't automatically update because we don't really do any real communication between the two. The easy solution would be to relax the check in the file API and just let the server communication explicitly tell the notebook if the file does not exist.

h/t @teonbrooks