add_buf

# File lib/csv.rb, line 917
    def add_buf
      if @is_eos
        return false
      end
      begin
        str_read = read(BufSize)
      rescue EOFError
        str_read = nil
      rescue
        terminate
        raise
      end
      if str_read.nil?
        @is_eos = true
        @buf_list.push('')
        @buf_tail_idx += 1
        false
      else
        @buf_list.push(str_read)
        @buf_tail_idx += 1
        true
      end
    end