glTF fails (sparse accessors without base buffer view)

@waleguene

I believe this is the exact same issue as here, you can see my answer for the potential cause : https://github.com/KhronosGroup/glTF-Sample-Viewer/issues/404
(the fail can be replicated with the file in the issue as well)

Up!

The issue is still there on Sketchfab (glTF Sample Viewer made the fix since then).
Processing failure: Log in to your Sketchfab account - Sketchfab