Packing list import tool updates existing shipment items in other shipments when pallet name is not provided

[jmiranda]

The code that detects whether a shipment item already exists for a given line item only checks whether the inventory item (e.g. lot number, product pair) exists within a container (not a container within a shipment). In the case where container is not provided (e.g. null) then the code will match against any shipment item for the given lot number / product pair, which means that it could update existing shipment items in old shipments. The workaround is to always provide a pallet name in the Excel spreadsheet used to import.