When open the persona editor only the first time, the OnAnimChanged event is called with the argument none asset

OnAnimChanged did not seem to work correctly only the first time when opening the anim sequence and a PreviewScene was created. The OnAnimChanged event is supposed to notify which anim was changed, but it is "none" for the first time. Once a PreviewScene is opened and another animsequence is opened, the notification is correct. This is because "AnimAsset == GetPreviewAnimationAsset()" in the FAnimationEditorPreviewScene::SetPreviewAnimationAsset results in "none" animation. 

1. Open the udn project (this uses subsystem to bind RegisterOnAnimChanged with OnPreviewSceneCreated of PersonaPreviewScene)
2. Open the "FP_Idle" AnimSequence asset

Result:

Output log "OnAnimChanged: None

Expected:

Output log "OnAnimChanged: FP_Idle