If a PDF is included in search results, link directly to the file instead of the attachment page

gistfile1.php

<?php if ( have_posts()) : while (have_posts() ) : the_post(); ?>
	<div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
		<?php 
			$permalink = get_permalink();
			if( 'attachment' == get_post_type() ) {
				// if the result is a PDF, link directly to the file not the attachment page
				$permalink = wp_get_attachment_url( $post->ID );
			}
		?>
		<h2>
			<a href="<?php echo esc_url( $permalink ); ?>"><?php the_title(); ?></a>
		</h2>
		<?php the_excerpt(); ?>
	</div>
<?php endwhile; else : ?>
	<p>There were no posts found.</p>
<?php endif; ?>