[FIX] sale_product_configurator: error when editing configurable lines

PR #134787 was introduced to fix an error with product template
attribute values. However, when moving `ptavId.concat` into the if
statement, it missed the fact that the function returns a copy rather
than editing in place.

This means that the line achieved nothing.

opw-3513820

closes odoo/odoo#136216

X-original-commit: 3b823f0ba76b53d59cd6702836bef40ab3f484cb
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>
Signed-off-by: Andrew Gavgavian (andg) <andg@odoo.com>

addons/sale_product_configurator/static/src/js/sale_product_field.js

@@ -100,7 +100,7 @@ patch(SaleOrderLineProductField.prototype, {
              * no_variant and custom attribute don't need to be given to the configurator for new
              * products.
              */
-            ptavIds.concat(this.props.record.data.product_no_variant_attribute_value_ids.records.map(
+            ptavIds = ptavIds.concat(this.props.record.data.product_no_variant_attribute_value_ids.records.map(
                 record => record.resId
             ));
             /**