Undo project removal on error #4916
Description
I encountered this case today and am unsure how serious it is as a bug.
In the case of collaborative projects, it is possible that other users create files that you, the project owner, cannot delete. If you try and delete a project that you own (so you should be able to), and it encounters an error, it has already removed it from the lookup table and so there is no easy way to tell the file owner to delete those files and try again. Instead we get 'lost' projects, which can only be deleted from the command line or files app, as they do not appear on their owner's lookup table.
My thinking is that it might be more clear if we restore the lookup table if we encounter an error deleting the files, though would have to detect these errors before we start deleting stuff otherwise we can end up with partially deleted projects (like we do now).
At least nothing breaks in the current implementation, as once the manifest is removed (which is always possible) the partially deleted project can't be opened by anybody, so no bugs can be encountered.