Adding new entity may break entity.show

[mramato]

Add reported on the forum, hiding all entities and then adding a new one can cause some entities to reappear. Here's a Sandcastle example that shows the problem (hit Hide and then Add Entity).

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

var greenPolygon = viewer.entities.add({
    name : 'Green extruded polygon',
    polygon : {
        hierarchy : Cesium.Cartesian3.fromDegreesArray([-108.0, 42.0,
                                                        -100.0, 42.0,
                                                        -104.0, 40.0]),
        extrudedHeight: 500000.0,
        material : Cesium.Color.GREEN
    }
});

var bluePolygon = viewer.entities.add({
    name : 'Blue polygon with holes and outline',
    polygon : {
        hierarchy : {
            positions : Cesium.Cartesian3.fromDegreesArray([-99.0, 30.0,
                                                            -85.0, 30.0,
                                                            -85.0, 40.0,
                                                            -99.0, 40.0]),
            holes : [{
                positions : Cesium.Cartesian3.fromDegreesArray([
                    -97.0, 31.0,
                    -97.0, 39.0,
                    -87.0, 39.0,
                    -87.0, 31.0
                ]),
                holes : [{
                    positions : Cesium.Cartesian3.fromDegreesArray([
                        -95.0, 33.0,
                        -89.0, 33.0,
                        -89.0, 37.0,
                        -95.0, 37.0
                    ]),
                    holes : [{
                        positions : Cesium.Cartesian3.fromDegreesArray([
                            -93.0, 34.0,
                            -91.0, 34.0,
                            -91.0, 36.0,
                            -93.0, 36.0
                        ])
                    }]
                }]
            }]
        },
        material : Cesium.Color.BLUE,
        outline : true,
        outlineColor : Cesium.Color.BLACK
    }
});

Sandcastle.addToolbarButton('Hide', function(){
    viewer.entities.values.forEach(function (entity) {
        entity.show = false;
    });

});

Sandcastle.addToolbarButton('Add entity', function(){
    viewer.entities.add({
        name : 'AADA',
    position : Cesium.Cartesian3.fromDegrees(-65.59777, 35.03883),

    polygon : {
        hierarchy : Cesium.Cartesian3.fromDegreesArray([-115.0, 40.0,
                                                        -125.0, 35.0]),
        material : Cesium.Color.RED
    }
    });
});

viewer.zoomTo(viewer.entities);