Php Rest response if statment

The following code is used on a php page and works well. My only problem is when the url is submitted and the artist parameter isnt clean it dosent return information, instead it returns this:

<lfm status="failed"><error code="6">
    The artist you supplied could not be found
</error></lfm>

When it returns this I would like it to not continue the process. So i need some sort of if statement to check the response but I cant seem to code it properly. Thanks.

<table valign="top" width="90%" style="background-color:#fff; padding:0px 15px; border:1px solid ``#eae7e7;"><tr><th align="center" width="100%"><strong>Similar Artists</strong></th></tr><tr></tr>

<?php 

$url = "http://ift.tt/1nZjbT3";
if (!file_exists($url)) {
$xml=simplexml_load_file("$url");
if ($url === false) {
  // error!

}else{

foreach($xml->similarartists->artist as $artist){

foreach($artist->name as $name) {
$image = $artist->image;


$link = str_replace(' ', '-', $name); 

echo "<tr><th width='60%'><a href='http://ift.tt/1sLisww'>$name</a></th><th width='40%'><img src='$image' alt='$name' height='50' width='50'> </th></tr><tr><th> </th></tr>";
}
}
}

}else{
}
?>
</table>