Update tileset transform on get bounding sphere

[hpinkos]

This calls root.updateTransform when the bounding sphere is fetched instead of when modelMatrix is set. This fixes a case where I was calling viewer.flyTo(tileset) after the root.transform was updated but a render hadn't occurred yet, resulting in the bounding sphere being out of sync with the tileset position.

[cesium-concierge]

Thanks for the pull request @hpinkos!

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[lilleyse]

I agree on adding this to the bounding sphere getter, but why does it have to be removed from model matrix? Could both call updateTransform?

[hpinkos]

@lilleyse I suppose it doesn't have to be removed, but looking at that inline comment it looked like the only reason it was there was to update the bounding sphere for calls used by viewer.flyTo so I don't think it's necessary to have it both places. Is there a benefit to keeping it there?

[lilleyse]

Hm, yeah I suppose that's the only case I can think of too. Looks good.

[mramato]

Do you think this could be what was causing #6898?

[hpinkos]

@mramato I don't think so. This was really only causing problems if you changed the root transform and called 'fly to' before the next frame update. I don't think you were changing the transform when you encountered that issue.