Cannot set show: false for ground polyline entity

[hpinkos]

Setting polyline.show = false results in a crash.

var viewer = new Cesium.Viewer('cesiumContainer');

var entity = viewer.entities.add({
    polyline : {
        positions : Cesium.Cartesian3.fromDegreesArray([-75, 35,
                                                        -125, 35]),
        width : 5,
        material : Cesium.Color.RED,
        clampToGround : true
    }
});

Sandcastle.addToolbarButton('Show false', function() {
    entity.polyline.show = false;
});

viewer.zoomTo(viewer.entities);

@likangning93

[mramato]

I changed this to next release because it's a pretty blatant bug for a commonly used feature.