[hotfix] addon-cached-file-lookup-download-path-to-url

Corrects error preventing the user from viewing dropbox/dataverse files.

```
Stacktrace (most recent call last):

  File "framework/routing/__init__.py", line 96, in wrapped
    data = fn(*args, **kwargs)
  File "website/project/decorators.py", line 138, in wrapped
    return response or func(*args, **kwargs)
  File "website/project/decorators.py", line 181, in wrapped
    return func(*args, **kwargs)
  File "website/addons/dropbox/views/crud.py", line 174, in dropbox_view_file
    rendered = render_dropbox_file(file_obj, client=client, rev=rev)
  File "website/addons/dropbox/utils.py", line 166, in render_dropbox_file
    download_path=file_obj.download_url(guid=True, rev=rev),
```