问如何处理 Error on line 2 at column 1: Extra content at the end of the document？

$lng=$_GET['lng'];
$lat=$_GET['lat'];
$conn=new LoginSystem();
$conn->connect();
$dom = new DOMDocument("1.0");

$query="select catch_id,catch_details,image from mycatch where longitude='$lng' AND latitude='$lat'";
$result = mysql_query($query);

if (!$result) {
  die("Invalid query: " . mysql_error());
}

header("Content-type: text/xml");

// Iterate through the rows, adding XML nodes for each
while ($row = @mysql_fetch_assoc($result)){
  $node = $dom->createElement("mycatch");
  $node = $dom->appendChild($node);
foreach ($row as $fieldname => $fieldvalue) {
      $child = $dom->createElement($fieldname);
    $child = $node->appendChild($child);
    $value = $dom->createTextNode($fieldvalue);
    $value = $child->appendChild($value);
  }
}

$conn->disconnect();
$xml_string = $dom->saveXML();
echo $xml_string;