Handle fetch product data from data stores that don't extend WC_Product_Data_Store_Custom_Table

[pcfreak30]

\WC_Product_Data_Store_CPT::read_product_data calls $post_meta_values = get_post_meta( $id ); which needs to fetch everything.

However, since extensions extend this and not WC_Product_Data_Store_Custom_Table we need to intercept this to return the core data + all other meta as it expects.