Only force camera above terrain when loading is finished.
Only force camera above terrain when loading is finished.

Fixes #6962

I'm not sure if we introduced a regression somewhere or if we just never
noticed, but the desired camera behavior is that it not force the view to
be above terrain if there is still terrain loading.  I also confirmed
that #4075 is still fixed even with this change.

CesiumGS/cesium,jasonbeverage/cesium,hodbauer/cesium,likangning93/cesium,hodbauer/cesium,josh-bernstein/cesium,likangning93/cesium,YonatanKra/cesium,likangning93/cesium,hodbauer/cesium,YonatanKra/cesium,AnalyticalGraphicsInc/cesium,kaktus40/cesium,soceur/cesium,CesiumGS/cesium,progsung/cesium,AnalyticalGraphicsInc/cesium,YonatanKra/cesium,geoscan/cesium,CesiumGS/cesium,likangning93/cesium,josh-bernstein/cesium,progsung/cesium,YonatanKra/cesium,soceur/cesium,likangning93/cesium,soceur/cesium,geoscan/cesium,CesiumGS/cesium,jasonbeverage/cesium,kaktus40/cesium,CesiumGS/cesium