display posts tag__in or latest if there are not enough result

Hello, I want to display 4 posts in ma page with tag__in parameter.
But if my query return less than 4 posts, because I only have 2 posts tagged, I wan’t to add my two latest post to always display 4 posts.
How can I do that please, whithout making multiple Wp_query ?
This is my working bad code :

$tag_ids = wp_get_post_tags( $post->ID, array( 'fields' => 'ids' ) );
$args = array(
'posts_per_page' => 4,
'cat' => 5,
'post__not_in'=> array($post->ID),
'tag__in'=> $tag_ids
);
$query = new WP_Query($args);
$nbposts = $query->post_count;
$ids = array($post->ID);

while ( $query->have_posts() ) : $query->the_post();
$ids[] = get_the_ID();

... my post content

endwhile;  wp_reset_postdata();

if($nbposts < 4){
$nbpost = 4 - $nbposts;
$args['posts_per_page'] = $nbpost;
$args['post__not_in'] = $ids;
$args['tag__in'] = '';
$query = new WP_Query($args);
while ( $query->have_posts() ) : $query->the_post();

... my post content

endwhile; wp_reset_postdata();

}