Test origin from sale instead of line to calculate cost for return sale of product kit

Closes #14854
(grafted from 7e5197d5a61cb5090d8a2c00ae4a12a25924aeda)

--HG--
branch : 8.0

modules/product_kit/stock.py

@@ -122,8 +122,8 @@ class MoveSale(metaclass=PoolMeta):
                 and self.origin.quantity < 0
                 and self.from_location.type != 'storage'
                 and self.to_location.type == 'storage'
-                and isinstance(self.origin.line.origin, Sale)):
-            sale = self.origin.line.origin
+                and isinstance(self.origin.line.sale.origin, Sale)):
+            sale = self.origin.line.sale.origin
             cost = Decimal(0)
             qty = Decimal(0)
             for move in sale.moves: