Comments: Avoid PHP notice in get_comment_reply_link() for null comment.

If there is no global comment, or the input comment is null, return early to prevent warnings.

Fixes #41846
Props birgire, earnjam



git-svn-id: https://develop.svn.wordpress.org/trunk@46335 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment-template.php

@@ -1646,6 +1646,10 @@ function get_comment_reply_link( $args = array(), $comment = null, $post = null
 
 	$comment = get_comment( $comment );
 
+	if ( empty( $comment ) ) {
+		return;
+	}
+
 	if ( empty( $post ) ) {
 		$post = $comment->comment_post_ID;
 	}