Metabox with sidebars dropdown

<?php
/*
Plugin Name: Custom Sidebars
*/

add_action('add_meta_boxes', 'sidebar_meta_boxes');

function sidebar_meta_boxes()
{
    add_meta_box( 'sidebar_metabox-1', __( 'Custom sidebar' ), 'sidebar_meta_box_content', 'page', 'normal', 'high');
}

function show_custom_sidebar($post_id = 0)
{
    global $post;

    // No post ID
    if ($post_id < 1) {
        $post_id = get_the_ID();
    }

    $sidebar = get_post_meta($post_id, 'menu-sidebar', true);

    if ( !empty($sidebar) ) {
        dynamic_sidebar($sidebar);
    }
}

// }}}
// {{{

function sidebar_meta_box_content()
{
    global $post;
    global $wp_registered_sidebars;

    $selected = get_post_meta($post->ID, 'menu-sidebar', true);

    wp_nonce_field('sidebar_save', 'sidebar_nonce');
    ?>
  <div class="jaxtag">
  <div class="ajaxtag hide-if-no-js">
    <table style="width: 100%">
        <tr>
            <td width="25%">
            <label for="menusidebar"><?php _e('Menu sidebar') ?>:</label>
            <label class="screen-reader-text" for="menusidebar"><?php _e('Menu sidebar') ?>:</label>
            </td>
            <td width="75%">
            <select name="menusidebar" id="menusidebar">
                <?php foreach ($wp_registered_sidebars as $sidebar) : ?>
                <option value="<?php echo $sidebar['id'] ?>" <?php echo (($selected == $sidebar['id']) ? 'selected="selected"' : '') ?>><?php echo $sidebar['name'] ?></option>
                <?php endforeach ?>
            </select>
            </td>
        </tr>
    </table>
  </div>
  </div>

    <?php
}


add_action('save_post', 'sidebar_save_postdata', 10, 2);

function sidebar_save_postdata( $post_id )
{
    global $wpdb;

    if ( !wp_verify_nonce( $_POST['sidebar_nonce'], 'sidebar_save' ) ) {
        return $post_id;
    }

    if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE ) {
        return $post_id;
    }

    // Check permissions ....

    /*
     * Sidebar
     */
    $menusidebar = trim($_POST['menusidebar']);

    if ( !empty($menusidebar) ) {
        update_post_meta($post_id, 'menu-sidebar', $menusidebar);
    }
}