fix: handle empty comment_type in email formatting (#177)

WordPress stores regular comments with comment_type as either empty
string or 'comment'. The strict === 'comment' check missed empty
strings, causing regular comments to be formatted as pingbacks/trackbacks
in notification emails. Now checks against known non-comment types instead.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: jdevalk

inc/clean-emails.php

@@ -181,7 +181,7 @@ private function add_comment_basics(): void {
 	 * @return void
 	 */
 	private function add_author_line(): void {
-		if ( $this->comment->comment_type === 'comment' ) {
+		if ( $this->comment->comment_type !== 'pingback' && $this->comment->comment_type !== 'trackback' ) {
 			/* translators: %1$s is replaced with the comment author's name, %2$s is replaced with the comment author's email */
 			$this->message .= \sprintf( \esc_html__( 'Author: %1$s (%2$s)', 'yoast-comment-hacks' ), \esc_html( $this->comment->comment_author ), '<a href="' . \esc_url( 'mailto:' . $this->comment->comment_author_email ) . '">' . \esc_html( $this->comment->comment_author_email ) . '</a>' ) . '<br />';
 		}
@@ -197,7 +197,7 @@ private function add_author_line(): void {
 	 * @return void
 	 */
 	private function add_content_line(): void {
-		if ( $this->comment->comment_type === 'comment' ) {
+		if ( $this->comment->comment_type !== 'pingback' && $this->comment->comment_type !== 'trackback' ) {
 			$this->message .= \esc_html__( 'Comment:', 'yoast-comment-hacks' );
 		}
 		else {