Fixed potential NaN probability in IDS unfolding
If two empty bins were considered when unfolding with IDS, the probability would be undefined due to a division by 0. This case is now checked, and a probability of 0 is returned instead of NaN.
If two empty bins were considered when unfolding with IDS, the probability would be undefined due to a division by 0. This case is now checked, and a probability of 0 is returned instead of NaN.