[FIX] sale_margin: no uom on line.

Since the purchase_price is now computed, it may be triggered before an
uom is set on the product line (onchanges may happen after computes).

closes odoo/odoo#41808

X-original-commit: 9ebbdd24752a0ff1c1057fc533074555810ffa39
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

addons/sale_margin/models/sale_order.py

@@ -18,7 +18,7 @@ class SaleOrderLine(models.Model):
             product_cost = product.standard_price
             fro_cur = product.cost_currency_id
             to_cur = line.currency_id or line.order_id.currency_id
-            if line.product_uom != product.uom_id:
+            if line.product_uom and line.product_uom != product.uom_id:
                 product_cost = product.uom_id._compute_price(
                     product_cost,
                     line.product_uom,