CodeIgniter query built with select_sum() incorrectly returns 1 from num_rows() when no qualifying records

Why does my script always say that a row is in the result set even if there where no qualifying records?

$this->db->select_sum('score_0')
    ->select_sum('score_1')
    ->select_sum('score_2')
          ..........
    ->select_sum('score_97')
    ->select_sum('score_98')
    ->select_sum('score_99');
$this->db->where('score_game_id',$game_id);
$this->db->order_by('score_id','asc');
$query = $this->db->get($this->tbl_lotteryApp_scores_twodigit);     
if ($query->num_rows() > 0){

}

I think this is the best solution for this situation:

function sum_score($game_id){
    if($this->check_for_scores($game_id)==true)
    {
        $this->db->select_sum('score_0')
        ->select_sum('score_1')
        ->select_sum('score_2')
              ...........
        ->select_sum('score_98')
        ->select_sum('score_99');
        $this->db->where('score_game_id',$game_id);
        $this->db->order_by('score_id','asc');
        $query = $this->db->get($this->tbl_lotteryApp_scores_twodigit);     
        return  $query->result();
    }

}

function check_for_scores($game_id)
{
    $this->db->where('score_game_id',$game_id);
    $this->db->order_by('score_id','asc');
    $query = $this->db->get($this->tbl_lotteryApp_scores_twodigit);     
    if ($query->num_rows() > 0){    
        return true;
    }else{
        return false;
    }
}

This worked for me :)