Fix vertical rhumb line when using PolylineGeometry

[baothientran]

Fixes #8764

The issue is that when two endpoints have the same longitude and latitude but different height, the math to calculate the number of points on rhumb line will return 0.

@lilleyse can you please take a look at it? Please let me know if I need to add anything

[cesium-concierge]

Thanks for the pull request @baothientran!

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Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[hpinkos]

Thanks @baothientran! I'll merge as soon as CI passes

[baothientran]

@hpinkos thank you for fixing my mistakes. I should be more careful about it in the future