The only way is to count them or (re)request them via WP_Query. I think I prefer the first solution because it's the less complex.
<?php if (have_posts()) : ?>
<?php
// We change the definition of the array to be able to store the count of each post_type
$types = array('post' => 0, 'videos' => 0, 'graphics' => 0, 'photos' => 0);
while (have_posts()) {
the_post();
// We check that only allowed post_type are counted
if (array_key_exists(get_post_type(), $types)) {
$types[get_post_type()]++;
}
}
?>
<?php foreach ($types AS $type => $nb_of_type) : ?>
<?php // We only show post_types that have at least one result ?>
<?php if ($nb_of_type > 0) : ?>
<div class="card">
<div class="card-header">
<h4><?= $type; ?></h4>
</div>
<div class="card-body">
<?php while (have_posts()) : the_post(); ?>
<?php if (get_post_type() === $type) : ?>
<?php get_template_part('template-part/content', $type); ?>
<?php endif; ?>
<?php endwhile; ?>
</div>
</div>
<?php endif; ?>
<?php endforeach; ?>
<?php endif; ?>
