function recoverCellIndex(rowIndex, cellIndex) {
    if (!_virtualTable[rowIndex]) {
      return cellIndex;
    }
    if (!_virtualTable[rowIndex][cellIndex]) {
      return cellIndex;
    }

    let newCellIndex = cellIndex;
    while (_virtualTable[rowIndex][newCellIndex]) {
      newCellIndex++;
      if (!_virtualTable[rowIndex][newCellIndex]) {
        return newCellIndex;
      }
    }
  }
Recover free index of row to append Cell.

@param {int} rowIndex Index of row to find free space.
@param {int} cellIndex Index of cell to find free space in table.