Add Icon to Post Title for Genesis

functions.php

add_filter('genesis_post_title_output', 'lunarwp_add_icon_to_post_title', 10, 1);
/**
 * Add icon to the Post Title
 *
 * @since  1.0.0
 * 
 * @param  string $title Post Title HTML
 * @return string        Amended Post Title HTML
 */
function lunarwp_add_icon_to_post_title( $title ) {
	$categories = get_the_category();
	
	if ( empty( $categories ) ) return $title;
	
	foreach ( $categories as $category ) {	
		$icon = sprintf( '<span class="icon-cat-%s"></span>', $category->slug );
		break;
	}

	if ( false === strpos( $title, 'rel="bookmark"' ) ) {
		$title = str_replace( 'itemprop="headline">', 'itemprop="headline">' . $icon, $title );
	} else {
		$title = str_replace( 'rel="bookmark">', 'rel="bookmark">' . $icon, $title );
	}
	
	return $title;
}

Added lines 12 & 14 and replaced the foreach with $categories - this will eliminate the error that can occur if there are no categories for a given article.

Line 13 - Added the missing closing parenthesis.