Comment 5 for bug 1743608

Fix pushed:

http://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/berick/lp1743608-user-edit-null-cards

I was able to replicate the NULL barcode scenario, but not the scan/double barcode scenario. However, the fix I pushed should address both. It enforces a single-barcode-replacement-per-edit-session rule. Any time Replace Barcode is clicked (accidentally or otherwise), any previous replacement barcodes for the current session are discarded before the new pending barcode is created.