Switch to 32-bit indices when we have more than 65536 vertices.
Switch to 32-bit indices when we have more than 65536 vertices.

likangning93/cesium,progsung/cesium,CesiumGS/cesium,AnalyticalGraphicsInc/cesium,YonatanKra/cesium,CesiumGS/cesium,likangning93/cesium,YonatanKra/cesium,CesiumGS/cesium,CesiumGS/cesium,progsung/cesium,likangning93/cesium,YonatanKra/cesium,CesiumGS/cesium,likangning93/cesium,likangning93/cesium,AnalyticalGraphicsInc/cesium,YonatanKra/cesium