def getNextCluster(clus)
      nxt = getFatEntry(clus)
      return nil if nxt > CC_END_OF_CHAIN
      raise "Damaged cluster in cluster chain" if nxt == CC_DAMAGED
      [nxt, getCluster(nxt)]
    end
def getNextCluster(clus)
      nxt = getFatEntry(clus)
      return nil if nxt > CC_END_OF_CHAIN
      raise "Damaged cluster in cluster chain" if nxt == CC_DAMAGED
      [nxt, getCluster(nxt)]
    end
Gets data for the next cluster given current, or nil if end.