[18.0][FIX] pos_lot_barcode: Collapse product array when length > 0

[mkoeck]

When scanning a lot/serial barcode that resolves to exactly one stock.lot, _getProductByLotBarcode fetches the related product.product via:

product = await this.pos.data.searchRead("product.product", ...);

searchRead always returns an array. The current code only collapses the result when length > 1, so when length === 1 the variable product remains an Array and is returned as such.

Upstream, _barcodeLotAction checks:

if (product instanceof Array) {
    // treat as multiple lots, build a names string
    const productNamesString = product
        .map(
            (lot) => this.pos.models["product.product"].get(lot.product_id).name
        )
        .join(", ");
    ...
}

This branch assumes an array of lots (with product_id), but it actually receives an array of products. That mismatch raises an exception while accessing lot.product_id and then .name on an undefined lookup.

Current behavior before PR

• Scanning a lot barcode that maps to one lot whose product isn’t yet cached in the POS frontend:
  • The function returns a one-item product array.
  • _barcodeLotAction treats it as multiple lots and executes the mapping above.
  • An exception is raised while building productNamesString instead of adding the product line because a product object does not have a product_id attribute, therefore this.pos.models["product.product"].get fails to look up the product

Desired behavior after PR is merged

• Single-item results from searchRead("product.product", ...) are collapsed to a record (product = product[0]).
• _barcodeLotAction receives a product record (not an array) and proceeds to add the product to the order.
• If the search returns no records (length === 0), _getProductByLotBarcode correctly returns false (“not available in POS”).