Specifying a flyTo pitch of -90 degrees causes crazy flights

[mramato]

Run the below example. With the 2000 range value it goes crazy. Change it to 0 and everything works nicely.

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

var entity = viewer.entities.add({
    position : Cesium.Cartesian3.fromDegrees(-95.0, 40.0),
    ellipse : {
        semiMajorAxis : 500.0,
        semiMinorAxis : 500.0,
        material : Cesium.Color.WHITE
    }
});

viewer.flyTo(entity, {
    offset: new Cesium.HeadingPitchRange(0, -Math.PI / 2, 2000)
});

Here's a similar issue that is probably the same bug

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

var latitude = 40.0;
var longitude = -100.0;
var north = latitude + .35;
var south = latitude - .35;
var east = longitude + 1.55;
var west = longitude - 1.55;
var rectangle = Cesium.Rectangle.fromDegrees(west, south, east, north);

var entity = viewer.entities.add({
    rectangle : {
        coordinates : rectangle,
        material : './static/Cesium_Logo_Color.jpg'
    }
});

viewer.flyTo(entity, {
    offset : new Cesium.HeadingPitchRange(0, -Math.PI / 2)
});

[WarpDrive]

Slightly offsetting pitch avoids the rolling flips

viewer.flyTo(entity, {
    offset: new Cesium.HeadingPitchRange(0, (-Math.PI / 2)+0.0000001, 2000)
});

viewer.flyTo(entity, {
    offset : new Cesium.HeadingPitchRange(0, (-Math.PI / 2)+0.0000001)
});

camera.direction doesn't have a horizontal component with vertical pitch, so there isn't really a heading of the direction vector in this case. Although I noticed in the new heading get code that the heading of the up vector is used instead when pitch is vertical.