If you don't want to display Warning when get_headers() function fails, you can simply add at-sign (@) before it.
<?php
// in failure, Warning will be hidden and false returned
$withoutWarning = @get_headers("http://www.some-domain.com");
// in failure, Warning displays and false will be returned, too
$withWarning = get_headers("http://www.some-domain.com");
// bool(false)
var_dump($withoutWarning);
// bool(false)
var_dump($withWarning);
?>