How to show min 1 post from specific categories/tax WP_Query?

I have custom query that shows specific number of posts from specific categories/tax.
Currently I limited the query to show posts from 2 categories , 3 and 4.
Issue I have is that the query can be limited to number of posts for example 4 than the query displays first 4 posts from category 3 never showing posts from category 4.

$args = array (
    'posts_per_page' => '4',
    'post__in' => array(),
    'post__not_in' => array(807),
    'author__in' => array(),
    'post_type' => array('post'),
    'paged' => 1,
    'tax_query' => array (
        'relation' => 'OR',
        array (
            'taxonomy' => 'category',
            'field' => 'term_id',
            'terms' => array(3,4),
        )
    ),
    'order' => 'DESC',
    'orderby' => 'date',
    'ignore_sticky_posts' => true,
    'date_query' => array(),
);

$query  = new WP_Query( $args );

How can I display specific number of posts from specific categories and show minimum one item from assigned categories?