[FIX] website_sale: prevent error when changing the delivery address

Currently, an error occurs when the user changing the delivery address in
the website.

Steps to reproduce:
- Install the website_sale module and enable the Demo payment provider.
- Go to Website > Shop > Add a product to Cart > View cart > Checkout.
- Ensure there are at least two different delivery addresses > Confirm > Pay now.
- Quickly press the browser’s back button twice.
- Select a different delivery address.

Error:
ValueError: Expected singleton: sale.order()

Root Cause:
At [1], the code calls order.ensure_one(). When the cart (sale.order) is empty,
leads to an error.

Fix:
This commit prevents a traceback on the frontend when a user attempts to
change the delivery address and safely redirects them to the shop page.

[1]:
https://github.com/odoo/odoo/blob/88c9a45ee1ff8dde871865723c3387c059af8289/addons/delivery/models/delivery_carrier.py#L157

sentry-6869972801

closes odoo#233326

X-original-commit: 2b57313
Signed-off-by: Valentin Chevalier <vcr@odoo.com>
Signed-off-by: Utsav Maru (utma) <utma@odoo.com>

Author: utma-odoo

addons/website_sale/static/src/interactions/checkout.js

@@ -33,6 +33,25 @@ export class Checkout extends Interaction {
         await this.waitFor(this._prepareDeliveryMethods());
     }
 
+    async start() {
+        // Monitor when the page is restored from the bfcache.
+        const boundOnNavigationBack = this._onNavigationBack.bind(this);
+        window.addEventListener("pageshow", boundOnNavigationBack);
+        this.registerCleanup(() => window.removeEventListener("pageshow", boundOnNavigationBack));
+    }
+
+    /**
+     * Reload the page when the page is restored from the bfcache.
+     *
+     * @param {PageTransitionEvent} event - The pageshow event.
+     * @private
+     */
+    _onNavigationBack(event) {
+        if (event.persisted) {
+            window.location.reload();
+        }
+    }
+
     /**
      * Set the billing or delivery address on the order and update the corresponding card.
      *