Use defaultdict to avoid KeyError

This can happen if all products from incoming moves are not in the inventory
moves. For example, if the quantity of an incoming move is set to zero.

issue6705
review43391002

stock.py

@@ -1,5 +1,7 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
+from collections import defaultdict
+
 from trytond.model import ModelView, Workflow
 from trytond.pool import Pool, PoolMeta
 
@@ -27,11 +29,8 @@ class ShipmentIn:
                         'in', move_ids),
                     ('purchase_request.origin', 'like', 'sale.sale,%'),
                     ])
-            pbl = {}
+            pbl = defaultdict(lambda: defaultdict(lambda: 0))
             for move in shipment.inventory_moves:
-                pbl.setdefault(move.product, {}).setdefault(
-                    move.to_location, 0.0)
-                pbl[move.product][move.to_location] += \
-                    move.internal_quantity
+                pbl[move.product][move.to_location] += move.internal_quantity
             for sale_line in sale_lines:
                 sale_line.assign_supplied(pbl[sale_line.product])