Bug 18611 - Create labels action fails in manage-marc-import.pl if an item has been...

Bug 18611 - Create labels action fails in manage-marc-import.pl if an item has been deleted from the import batch.

To test:
1 - Import a batch with some items
2 - Delete one of the imported items
3 - Browse to Tools->Staged MARC record management
4 - Click (Create label batch) for the batch you imported
5 - Recieve an error
6 - Apply patch
7 - Click (Create label batch)
8 - Batch is created with remaning items from the import

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Mason James <mtj@kohaaloha.com>