DynamicSunDefinition crashes with an index error looking up SolarElevation if it's NaN.

This happens if the player is standing on the exact opposite side of the planet, in alignment with the sun vector.

Exception occurred: VRage.MyUpdateSchedulerException: Failed to execute Void RunSingleFrame() on Medieval.MyMedievalGame
 ---> VRage.MyUpdateSchedulerException: Failed to execute Void FixedUpdate() on Medieval.GameSystems.DynamicEnvironment.MyDynamicEnvironmentSystem
 ---> System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
   at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
   at Medieval.GameSystems.DynamicEnvironment.DynamicProperties.Base.MyDynamicPropertyDefinitionBase.GetValue(Single key)
   at Medieval.GameSystems.DynamicEnvironment.MyDynamicEnvironmentSystem.DynamicPropertyData.Update(Single value, Single interpolationTime)
   at Medieval.GameSystems.DynamicEnvironment.MyDynamicEnvironmentSystem.FixedUpdate()
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates()