fix(storefront): SD-11524 Add to Cart and quantity buttons disabled on Integration store when BCData is empty

[bc-yevhenii-buliuk]

What?

This PR adds defensive validation before calling updateView() on product detail page initialization to prevent disabled Add to Cart and quantity +/- buttons when BCData.product_attributes is empty.

Problem
After merging PR #2601, Add to Cart and quantity +/- buttons are disabled on Integration store for simple product (without inventory tracking). The issue doesn't occur on Production/Staging.

PR #2601 removed the initial AJAX call and relies on BCData.product_attributes being populated on page load. On Integration store, this data is empty (BCData={}), causing updateView() to be called with empty data, which incorrectly triggers the disable logic in updateDefaultAttributesForOOS() method.

So we need to ensure that updateView() is only executed when actual product data is available.

Fixes the issue:
Buttons now work correctly on Integration store for simple products
No regression on Production/Staging environments
Variant selection continues to work properly (AJAX provides full data)

Known limitation:
When BCData.product_attributes is empty, out-of-stock UI features (disabled buttons, banners) may not display on initial page load. This is defensive behavior to prevent incorrect states from processing invalid data.

Requirements

• CHANGELOG.md entry added (required for code changes only)

Tickets / Documentation

• SD-11534

Screenshots (if appropriate)

• locally on integration store

integration_without_BCData.mov

• locally on staging store

staging_with_BCData.mov

[bc-alexsaiannyi]

makes sense to me. @bc-yevhenii-buliuk, what do you think if we add console.warn with a message that BCData is empty to improve DX little bit more?

[bc-alexsaiannyi]

👏