Tify crashes on 2.0 manifest with range without canvases

[Lukski]

I noticed that with a IIIF 2.0 manifest Tify crashes when there is a range defined that has viewingHint top set, but no canvases or other ranges included.
I prepared some examples here:

1. Range with canvases and viewingHint top; works but contents menu is empty: https://tify.rocks/?manifest=https%3A%2F%2Flgraf.uber.space%2Fmanifest_viewing_hint_canvas.json
2. viewingHint not set, no canvases; also works: https://tify.rocks/?manifest=https%3A%2F%2Flgraf.uber.space%2Fmanifest_no_viewing_hint_no_canvas.json
3. viewingHint top, but no canvases: breaks, does not display anything https://tify.rocks/?manifest=https%3A%2F%2Flgraf.uber.space%2Fmanifest_viewing_hint_no_canvas.json

I know this is not really a practical use case and I can understand if you do not support it.
We just had some clients who generated manifests like this and would appreciate being able to handle this case more gracefully