[Help Wordpress] Hiding the error

You can use a WP function to detect if any attachment...
In your template php:

$args = array(
    'post_type' => 'attachment',
    'numberposts' => null,
    'post_status' => null,
    'post_parent' => $post->ID
);
$attachments = get_posts($args);
if ($attachments) {
 echo do_shortcode( '[gallery royalslider="1"]' ) ;
}
?>

.

help.dimsemenov.com