Handling zero origin for localFrameToFixedFrame

[IanLilleyT]

Fixes #8570

#8475 exposed a bug where calling viewer.zoomTo(tileset) on a root tile (or any tile centered at zero) would crash. Ultimately this was caused by Transforms.eastNorthUpToFixedFrame not handling the zero vector case and returning a bad transformation matrix. Since ENU is not well defined at zero, I return the degeneratePositionLocalFrame matrix instead, which is similar to how the north and south pole are handled.

@loshjawrence

[cesium-concierge]

Thanks for the pull request @IanLilleyT!

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[lilleyse]

Nice, this fixes zooming to regions that cover the whole globe and bounding spheres at (0,0,0), both important for global 3D Tilesets.

[loshjawrence]

I can confirm it fixes it, I looked over the code and it seems fine.