[FIX] website_sale: remove animation when out-of-stock product is added

Steps to reproduce:
	1) Create a product with 0 on hand qty and under Sales tab,
	"Continue Selling" if Out of Stock unchecked.
	2) Navigate to the website's shop.
	Customize -> Add Feature -> enable Add to Cart.

Current behavior:
From the Shop's screen, the button to add to cart for this product
 is clickable and the animation plays, but no item is added (because
out of stock).

Expected behavior:
There is no animation when an out-of-stock product is added to the cart

This fix completes the fix at commit 8d3a4e1f7094ded889b652e5ec393f6eb2f2b6f6
that didn't take into account the possibility of an empty cart (0) that led to
an undefined value of card_quantity in the data returned from the rpc.

opw-2856711
opw-2745305

closes odoo/odoo#92578

X-original-commit: fdf97d84d1a331f3062bcda6707dfd8c3bc90532
Signed-off-by: William Braeckman (wbr) <wbr@odoo.com>

addons/website_sale/static/src/js/website_sale_utils.js

@@ -34,7 +34,7 @@ const cartHandlerMixin = {
             route: "/shop/cart/update_json",
             params: params,
         }).then(async data => {
-            if (data.cart_quantity !== parseInt($(".my_cart_quantity").text())) {
+            if (data.cart_quantity && (data.cart_quantity !== parseInt($(".my_cart_quantity").text()))) {
                 await animateClone($('header .o_wsale_my_cart').first(), this.$itemImgContainer, 25, 40);
                 updateCartNavBar(data);
             }