Erasure Coding: Update last cellsize calculation according to whether the erasure codec has chunk boundary

private static int lastCellSize(int size, int cellSize, int numDataBlocks,
      int i) {
    if (i < numDataBlocks) {
      // parity block size (i.e. i >= numDataBlocks) is the same as 
      // the first data block size (i.e. i = 0).
      size -= i*cellSize;
      if (size < 0) {
        size = 0;
      }
    }
    return size > cellSize? cellSize: size;
  }