WIP: Fixed checking of validity in RichRayTraceCherenkovCones

This has been discovered by chance, while playing with compilation flags. All of a sudden, I got plenty of messages like "WARNING NULL DeRichPD pointer !!" and "ERROR Track PD index out of range !!" in the logs. Chasing the problem I came to the conclusion that this change is needed. And it indeed fixes the messages. @jonrob can you confirm ?