Sales Orders: Bulk Edit Items Works Again When A Line Has No Product

Bulk editing items on a sales order was refusing to save whenever any existing line on the order had no product or SKU on it. That treated a saved line as invalid, so the Save button stayed disabled and no other edits on the order could be applied. Existing lines now validate by their order-item id, so a saved line without a product no longer blocks the rest of the changes. Newly added lines still require a product or a SKU.