Api settings image upload

Hi, I am creating api settings page. I have an logo upload option in page. My problem is, if I click upload button when the file upload field is empty, my option array looks like this a:3:{ s:5:”files”;s:5:”Array”;s:4:”file”;a:1:{s:5:”error”;s:21:”No file was uploaded.”;}}. I have written my full code below please help somebody.

<?php
/*
Plugin Name:Rough test
*/

//Logo Upload

	add_action('admin_init', 'ld_admin_init');
	function ld_admin_init() {
		register_setting( 'ld_options', 'ld_options', 'ld_options_validate' );
		add_settings_section('ld_main', 'Upload', 'ld_section_text', 'ld');
		add_settings_field('ld_setting_checkbox', 'Use image', 'ld_setting_checkbox', 'ld', 'ld_main');
		add_settings_field('ld_setting_string', 'Logo text', 'ld_setting_string', 'ld', 'ld_main');
		add_settings_field('ld_filename', 'File:', 'ld_setting_filename', 'ld', 'ld_main');
	}

// add the admin options page
	add_action('admin_menu', 'ld_admin_add_page');
	function ld_admin_add_page() {
		$mypage = add_theme_page('Logo', 'Logo', 'manage_options', 'ld', 'ld_options_page');
	}

// display the admin options page
	function ld_options_page() {

	?>
        <div class="wrap">
        <h2>Logo settings</h2>
        <p>You can upload a new logo.</p>
        <form method="post" enctype="multipart/form-data" action="options.php">
        <?php settings_fields('ld_options'); ?>
        <?php do_settings_sections('ld'); ?>
        <p class="submit">
        <input type="submit" name="Submit" class="button-primary" value="<?php esc_attr_e('Save Changes') ?>" />
        </p>
        </form>

        </div>

	<?php
	}

	function ld_section_text() {
		echo '<input type="hidden" name="ld_options[file]" value="' . serialize( $file ) . '" />';
		$options = get_option('ld_options');
		echo '<p>Upload your file here:</p>';
		if ($file = $options['file']) {
			//var_dump($file);
			echo "<img src='{$file['url']}' />";
		}
	}

	function ld_setting_filename() {
		echo '<input type="file" name="ld_filename" size="40" />';
	}

	function ld_setting_checkbox() {
		$usetext = get_option('ld_options');
		if($usetext['chkbox1']) { $checked = ' checked="checked" '; }
		echo "<input ".$checked." id='plugin_chk1' name='ld_options[chkbox1]' type='checkbox' />";
	}

	function ld_setting_string() {
		$logotext = get_option('ld_options');
		echo "<input id='ld_logo_text' name='ld_options[text_string]' size='40' type='text' value='{$logotext['text_string']}' />";
	}

	function ld_options_validate( $input ) {
		// set $newinput to the $input that was POSTed
		$newinput = $input;

		// update the file field
		if ($_FILES['ld_filename']) {
			$overrides = array('test_form' => false);
			$file = wp_handle_upload($_FILES['ld_filename'], $overrides);
			$newinput['file'] = $file;
		} else {
			$newinput['file'] = maybe_unserialize( $input['file'] );
		}

		return $newinput;
	}
?>