Query All users that has post

add this in your arguments 'query_id' => 'authors_with_posts',

    $user_args = array(
        'role'    => 'frontend_vendor',
        'orderby' => 'display_name', 
        'query_id' => 'authors_with_posts',
        'order'   => 'ASC',      
        'number'  => $no,
        'offset'  => $offset
    );