Problem with checkout of multi-piece item when it's not the first one

Overview: Found this bug by accident when Anya N. Arnold and I were testing UICHKOUT-446. If your try to check out the multi-piece after some non-multi-piece items, the checkout screen becomes unresponsive

Steps to Reproduce:

1. Log into FOLIO-testing as diku_admin
2. Go to Inventory
3. Find or create multiple item records, several with no piece info, and at least one with piece info
4. Go to Checkout, and checkout at least one non-piece-info item
5. Then check out an item with piece info

Expected Results: The multi-piece modal should display, and the item should be checked out

Actual Results: The checkout screen freezes, and after a while, you get a "page unresponsive" message from the browser

Additional Information: See attached video (part 1 and 2) with examples

Interested parties: ecboettcher