Add missing singular placeholder in comments.php

Fixes #1021.

comments.php

@@ -27,11 +27,27 @@
 	if ( have_comments() ) : ?>
 		<h2 class="comments-title">
 			<?php
-				printf( // WPCS: XSS OK.
-					esc_html( _nx( 'One thought on &ldquo;%2$s&rdquo;', '%1$s thoughts on &ldquo;%2$s&rdquo;', get_comments_number(), 'comments title', '_s' ) ),
-					number_format_i18n( get_comments_number() ),
-					'<span>' . get_the_title() . '</span>'
-				);
+				$comments_number = get_comments_number();
+				if ( 1 === $comments_number ) {
+					printf(
+						/* translators: %s: post title */
+						esc_html_x( 'One thought on &ldquo;%s&rdquo;', 'comments title', '_s' ),
+						'<span>' . get_the_title() . '</span>'
+					);
+				} else {
+					printf( // WPCS: XSS OK.
+						/* translators: 1: number of comments, 2: post title */
+						esc_html( _nx(
+							'%1$s thought on &ldquo;%2$s&rdquo;',
+							'%1$s thoughts on &ldquo;%2$s&rdquo;',
+							$comments_number,
+							'comments title',
+							'_s'
+						) ),
+						number_format_i18n( $comments_number ),
+						'<span>' . get_the_title() . '</span>'
+					);
+				}
 			?>
 		</h2>