file upload in admin panel wordpress

file upload do not work, why? and how can help me? file do not uploaded.

this is settings page

function ag_products_theme_settings_page(){
    ?>
    <div class="wrap">
    <h1>AG Products</h1>
    <form method="post" action="options.php" enctype="multipart/form-data">
        <?php
            settings_fields("section");
            do_settings_sections("theme-options");      
            submit_button(); 
        ?>          
    </form>
    </div>
<?php
}

this is part for displaying logo

function logo_display()
{
    ?>
        <input type="file" name="logo" /> 
        <?php echo get_option('logo');         
        ?>                      
   <?php
}

this is part for uploading logo

function handle_logo_upload()
{
    if(!empty($_FILES["demo-file"]["tmp_name"]))
    {           
        require_once( ABSPATH . 'wp-admin/includes/file.php' );
        $urls = wp_handle_upload($_FILES["logo"], array('test_form' => false));
        $temp = $urls['url'];
        return $temp;
    }       
    return $option;     

}

and this is for register

function ag_products_display_theme_panel_fields()
{
    add_settings_section("section", "All Settings", null, "theme-options");
    add_settings_field("logo", "Logo", "logo_display", "theme-options", "section");  


    register_setting("section", "logo", "handle_logo_upload"); 
}

add_action("admin_init", "ag_products_display_theme_panel_fields");

via Chebli Mohamed