Display Proper Author Information For Posts != $post->ID

When get_coauthors() is called with a post ID (`$post_id`) specified, `$post->ID`'s author is displayed if `$post_id` is created by a "real" user (non-coauthor), even if `$post_id != $post->ID`.

This corrects this functionality, and will display the current post's author if and only if `$post_id == $post->ID`.

template-tags.php

@@ -22,7 +22,7 @@ function get_coauthors( $post_id = 0 ) {
 					$coauthors[] = $post_author;
 			}
 		} else if ( !$coauthors_plus->force_guest_authors ) {
-			if ( $post ) {
+			if ( $post && $post_id == $post->ID ) {
 				$post_author = get_userdata( $post->post_author );
 			} else {
 				$post_author = get_userdata( $wpdb->get_var( $wpdb->prepare("SELECT post_author FROM $wpdb->posts WHERE ID = %d", $post_id ) ) );