Not tested, but from quick look something like this should work:
$comment = get_comment($commentID);
$post = get_post($comment->comment_post_ID);
$user = get_userdata($post->post_author);
if( $comment->user_id == $post->post_author )
return;
Not tested, but from quick look something like this should work:
$comment = get_comment($commentID);
$post = get_post($comment->comment_post_ID);
$user = get_userdata($post->post_author);
if( $comment->user_id == $post->post_author )
return;