Exception when canceling morph while flight in progress.

[mramato]

1. Run the Camera example.
2. Selected Fly to Location with heading, pitch, and roll
3. While in flight, switch to 2D or CV mode
4. Immediately click the canvas to complete the morph.

You'll get the following stack trace:

DeveloperError: lookAtTransform is not supported while morphing.
Error
   at DeveloperError (http://localhost:8080/Source/Core/DeveloperError.js:43:13)
   at Camera.prototype.lookAtTransform (http://localhost:8080/Source/Scene/Camera.js:1576:13)
   at Sandcastle.reset (Unknown script code:201:5)
   at Anonymous function (Unknown script code:209:5)
   at Event.prototype.raiseEvent (http://localhost:8080/Source/Core/Event.js:146:17)
   at complete2DCallback (http://localhost:8080/Source/Scene/SceneTransitioner.js:681:9)
   at completeMorph (http://localhost:8080/Source/Scene/SceneTransitioner.js:250:17)
   at handleMouseDown (http://localhost:8080/Source/Core/ScreenSpaceEventHandler.js:156:13)
   at handlePointerDown (http://localhost:8080/Source/Core/ScreenSpaceEventHandler.js:598:13)
   at listener (http://localhost:8080/Source/Core/ScreenSpaceEventHandler.js:66:13) (on line 1576 of http://localhost:8080/Source/Scene/Camera.js)

[mramato]

Turns out this is bug is specific to the camera Sandcastle example, but might be exposing a race condition with the morphComplete event in Cesium itself.

[mramato]

CC #2683

[emackey]

Load the Sandcastle Camera demo, and switch to Columbus View. This error appears at the end of the morph.

An error occurred while rendering. Rendering has stopped.
DeveloperError: lookAtTransform is not supported while morphing.
Error
    at new DeveloperError (http://cesiumjs.org/Cesium/Source/Core/DeveloperError.js:43:19)
    at Camera.lookAtTransform (http://cesiumjs.org/Cesium/Source/Scene/Camera.js:1576:19)
    at Object.Sandcastle.reset (<anonymous>:201:19)
    at <anonymous>:209:16
    at Event.raiseEvent (http://cesiumjs.org/Cesium/Source/Core/Event.js:146:30)
    at completeColumbusViewCallback (http://cesiumjs.org/Cesium/Source/Scene/SceneTransitioner.js:706:43)
    at Object.options.complete (http://cesiumjs.org/Cesium/Source/Scene/SceneTransitioner.js:598:17)
    at update (http://cesiumjs.org/Cesium/Source/ThirdParty/Tween.js:403:45)
    at TweenCollection.update (http://cesiumjs.org/Cesium/Source/Scene/TweenCollection.js:539:29)
    at Scene.initializeFrame (http://cesiumjs.org/Cesium/Source/Scene/Scene.js:1373:22)

[zoiclabs-userdev]

+1. The steps provided in #2683 are more accurate. Just switching breaks the app.