[ALS] Fix error when converting buffer to CSRNumericTable

[minmingzhu]

When converting buffer to CSRNumericTable, If multiple rows without non-zero elements, we only calculated once for rowOffsets Array.

for (i <- 0 until ratingsNum) {
      // Modify row index for each partition (start from 0)
      val row = buffer.getLong(i * RATING_SIZE) - getPartitionOffset(rankId, nFeatures, nBlocks)
      val column = buffer.getLong(i * RATING_SIZE + 8)
      val rating = buffer.getFloat(i * RATING_SIZE + 16)

      values(index) = rating
      // one-based index
      columnIndices(index) = column + 1

      if (row > curRow) {
        curRow = row
        // one-based indexValues
        rowOffsets += index + 1
      }

      index = index + 1
    }
    // one-based row index
    rowOffsets += index + 1