[wishlist]Force creating a wishlist for guest or user that without default wishlist.

functions.php

// Force creating a wishlist for guest or user that without default wishlist.
add_action( 'wp', 'tinvwl_set_sharekey' );

function tinvwl_set_sharekey() {

	// Check if Wihslist class loaded.
	if ( ! class_exists( 'TInvWL_Wishlist' ) ) {
		return;
	}

	// Get sharekey for a default wishlist.
	$wl       = new TInvWL_Wishlist();
	$sharekey = $wl->get_sharekey();

	// Create a wishlist in case it doesn't exists.
	if ( empty( $sharekey ) ) {
		$user_id  = get_current_user_id();
		$sharekey = $wl->add_user_default( $user_id );
	}
}