Register _wp_cron() to run on the {@see ‘wp_loaded’} action.

If the {@see ‘wp_loaded’} action has already fired, this function calls
_wp_cron() directly.

Warning: This function may return Boolean FALSE, but may also return a non-Boolean
value which evaluates to FALSE. For information about casting to booleans see the
{@link PHP documentation}. Use
the `===` operator for testing the return value of this function.

function wp_cron() {
	if ( did_action( 'wp_loaded' ) ) {
		return _wp_cron();
	}

	add_action( 'wp_loaded', '_wp_cron', 20 );
}