dedecms上传文件提示Field:1错误解决办法

$filename = './data/common.inc.php';

$contents = file_get_contents($filename);

$charset[1] = substr($contents, 0, 1);

$charset[2] = substr($contents, 1, 1);

$charset[3] = substr($contents, 2, 1);

if (ord($charset[1]) == 239 && ord($charset[2]) == 187 && ord($charset[3]) == 191){

$data = substr($contents, 3);

$filenum = fopen($filename, "w");

flock($filenum, LOCK_EX);

fwrite($filenum, $data);

fclose($filenum);

}