Store synchronized moves of customer shipment even when quantity is not updated

ed41959390ff added a synchronization on assign to prevent infinite warning
loop on pack if it creates new move without origin.
But 38e2a76db719 refactoring lost this behavior.

Closes #12503
(grafted from 903204d5d1728e818ec44bf5aa0a629c2efd1a65)

--HG--
branch : 6.0

modules/stock/shipment.py

@@ -1407,7 +1407,7 @@ class ShipmentOut(ShipmentAssignMixin, Workflow, ModelSQL, ModelView):
                         move.uom)
                     if quantity and move.quantity != qty:
                         move.quantity = qty
-                        moves.append(move)
+                    moves.append(move)
         Move.save(moves)
 
     @classmethod