updated PolylineVolumeGeometryLibrary.js to handle edge case
updated PolylineVolumeGeometryLibrary.js to handle edge case

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