Undefined offset in php

    include("config.php");

    include("header.php");
    include("commonfunctions.php");

    $file = file($irpg_db);
#    unset($file[0]);
    if (!$_GET['sort'] ||
        (($_GET['sort'] != "cmp_nick_asc") &&
        ($_GET['sort'] != "cmp_nick_desc") &&
        ($_GET['sort'] != "cmp_score_asc") &&
        ($_GET['sort'] != "cmp_score_desc") &&
        ($_GET['sort'] != "cmp_wins_asc") &&
        ($_GET['sort'] != "cmp_wins_desc") &&
        ($_GET['sort'] != "cmp_guesses_asc") &&
        ($_GET['sort'] != "cmp_guesses_desc"))) $_GET['sort'] = "cmp_nick_asc";
    usort($file,$_GET['sort']);
$file_corretto=array();
$file=array_map('trim',$file);
foreach($file as $chiave => $valore){
    if($valore != ""){
        $file_corretto[]=$valore;
    }
} 
[...]


    foreach ($file_corretto as $line) { list($nick,$guesses,$wins,$score, ) = explode(",",trim($line));

      echo "      <tr>\n".
           "        <td nowrap>$nick</td>\n".
           "        <td align=center>$score</td>\n".
           "        <td align=center>$wins</td>\n".
           "        <td align=center>$guesses</td>\n".
           "      </tr>\n";
    }

    echo('</table>');
    include("footer.php");

   function cmp_score_desc($a,$b) {
	        var_dump($a);
        var_dump($b); 
        list($nick1,$guesses1,$wins1,$score1)=explode(",",trim($a));
        list($nick2,$guesses2,$wins2,$score2)=explode(",",trim($b));
        if ($score1 == $score2) return ($wins2 <= $wins1) ? -1 : 1;
        return ($score1 > $score2) ? -1 : 1;
    }

puffetta,1,0,0
dotto,2,0,0
zorro,5,4,5
superman,1,0,0
hulk,4,1,1

$righe = file("db.txt");
 
foreach ($righe AS $key => $riga)
  {
  list($uno, $due, $tre, $quattro) = explode(",", $riga);
  if (strlen($uno) < 2) 
    unset($righe[$key]);
  }
$fp = fopen("db.txt", "w+");
foreach ($righe AS $key => $riga)
   fputs($fp, $riga);
fclose($fp);