Do not get product from last fifo moves but from self move

The fifo moves can be empty and so move is undefined.

issue7918

move.py

@@ -74,7 +74,7 @@ class Move(metaclass=PoolMeta):
         # Compute average cost price
         unit_price = self.unit_price
         self.unit_price = Uom.compute_price(
-            move.product.default_uom, cost_price, self.uom)
+            self.product.default_uom, cost_price, self.uom)
         average_cost_price = self._compute_product_cost_price('out')
         self.unit_price = unit_price