[FIX] website_sale: image in carousel

- Create a product with 3 variants
- Put a picture on the template, then on all variants but the first one
  (the one with computed for field `product_variant_id`)
- Check "Multi image" setting in website config

In the product page of the eCommerce, the carousel is not displayed.

This is because the template only checks if the first variant has an
image in order to display the carousel. It should check all variants.

opw-1823242

addons/website_sale/views/templates.xml

@@ -412,7 +412,7 @@
                         <div class="col-sm-7">
                             <span itemprop="image" t-attf-content="{{request.httprequest.url_root}}web/image/product.template/{{product.id}}/image" t-field="product.image" t-options="{'widget': 'image', 'class': 'product_detail_img', 'alt-field': 'name', 'zoom': 'image'}" groups="!website_sale.group_website_multi_image"/>
                             <t groups="website_sale.group_website_multi_image">
-                                <t t-set="variant_img" t-value="product.product_variant_id.image_variant"/>
+                                <t t-set="variant_img" t-value="any(product.mapped('product_variant_ids.image_variant'))"/>
                                 <t t-set="image_ids"  t-value="product.product_image_ids"/>
                                 <div id="o-carousel-product" class="carousel slide" data-ride="carousel" data-interval="0">
                                   <div class="carousel-outer">