An interrupted flight means the next flight will start part way through

[kring]

Reported here:
https://community.cesium.com/t/about-currentflytotime-in-cesiumflytocontroller/36701

When a CesiumFlyController flight completes, the _currentFlyToTime is reset to zero:
https://github.com/CesiumGS/cesium-unity/blob/v1.13.1/Runtime/CesiumFlyToController.cs#L312

But if the flight is interrupted, it is not:
https://github.com/CesiumGS/cesium-unity/blob/v1.13.1/Runtime/CesiumFlyToController.cs#L329

Starting a new flight also, surprisingly, does not reset _currentFlyToTime to zero, either. So as a result, an interrupted flight means that the next flight begins at whatever _currentFlyToTime the previous one was interrupted at.