[FIX] purchase_stock: fix price difference

1. Create a storable product
2. Set the category: Costing
   - Method: First In First Out (FIFO)
   - Inventory Valuation: Automated
   - Price Difference Account: Price different accounts.
3. Create a vendor bill with the product and the quantity set as 0, and set a tax
4. Post the vendor Bill

A ZeroDivision error is raised.

opw-2375464

closes odoo/odoo#62104

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/purchase_stock/models/account_invoice.py

@@ -116,7 +116,7 @@ class AccountMove(models.Model):
 
 
                 price_unit = line.price_unit * (1 - (line.discount or 0.0) / 100.0)
-                if line.tax_ids:
+                if line.tax_ids and line.quantity:
                     # We do not want to round the price unit since :
                     # - It does not follow the currency precision
                     # - It may include a discount