Consolidated WebGL fixes into a single fix [skip ci]
Consolidated WebGL fixes into a single fix [skip ci]

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