Sends a JSON response back to an Ajax request, indicating failure.

If the `$data` parameter is a WP_Error object, the errors
within the object are processed and output as an array of error
codes and corresponding messages. All other types are output
without further processing.

function wp_send_json_error( $data = null, $status_code = null, $options = 0 ) {
	$response = array( 'success' => false );

	if ( isset( $data ) ) {
		if ( is_wp_error( $data ) ) {
			$result = array();
			foreach ( $data->errors as $code => $messages ) {
				foreach ( $messages as $message ) {
					$result[] = array(
						'code'    => $code,
						'message' => $message,
					);
				}
			}

			$response['data'] = $result;
		} else {
			$response['data'] = $data;
		}
	}

	wp_send_json( $response, $status_code, $options );
}