Fixed ill defined track Chi2ndof for ndof=0.
This is e.g. the case, when the tripplett method. Changed ndof type to size_t. Track derived classes now return Chi2ndof = -1 if ndof <= 0. This used to be incoherent between derived classes.
This is e.g. the case, when the tripplett method. Changed ndof type to size_t. Track derived classes now return Chi2ndof = -1 if ndof <= 0. This used to be incoherent between derived classes.