Using Camera.lookAt followed by camera.setView breaks mouse controls

It looks like by doing the following, the camera.position will be set to (0, 0, 0) and then trying to adjust the camera using the mouse will cause a failure:
```JavaScript
viewer.camera.lookAt(Cesium.Cartesian3.fromDegrees(15, 0, 100), new Cesium.HeadingPitchRange(0, 0, 100));
viewer.camera.setView({destination: Cesium.Cartesian3.fromDegrees(15, 0, 100)});

// then try to adjust the camera using the mouse
```

Using sandcastle it gives this error:
```
DeveloperError: normalized result is not a number
DeveloperError@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:540:19
Cartesian3.normalize@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:8139:19
rotateVertical@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:188049:17
Camera.prototype.rotateUp@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:188040:9
rotate3D@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:233530:13
spin3D@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:233409:13
reactToInput@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:232513:21
update3D@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:234040:9
ScreenSpaceCameraController.prototype.update@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:234075:13
Scene.prototype.initializeFrame@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:239589:9
CesiumWidget.prototype.render@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:250532:13
render@https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js:249915:25
```

Reproduce the failure in Sandcastle with the reported camera.lookAt, camera.setView, and mouse-control sequence. Start from the stack entries for Camera.prototype.rotateUp, rotateVertical, and Cartesian3.normalize; done means the same sequence leaves mouse controls usable without the “normalized result is not a number” error.

Written by the indexing model from the issue text.