Fix Rectangle.union when rectangle spans entire globe

[IanLilleyT]

The code used to call CesiumMath.convertLongitudeRange which

converts a longitude value, in radians, to the range [-Math.PI, Math.PI)

So when the rectangle.east equals Math.PI, it will get converted to -Math.PI. If the rectangle spans the entire globe, this creates a rectangle that has 0 width.

I replaced it with CesiumMath.negativePiToPi which returns

the angle in the range [-CesiumMath.PI, CesiumMath.PI]

Sandcastle demonstrating the fix

[cesium-concierge]

Thanks for the pull request @IanLilleyT!

• ✔️ Signed CLA found.

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