Iterate over valid samples in the Occupancy map to find "holes", ie pixels where no valid sample could be computed according to IsValidSampleFunction. This can be used after a bake to find locations where the baked map needs to be repaired as a post-process (eg using image infilling/etc), which can produce better results than (eg) using a "worse" sampling strategy to guarantee some non-garbage result (eg Nearest-point sampling)