Rec-Vend Pen entry duplication

### Testmerges

#5724: 'XM43E1 in regular gameplay' by Releasethesea at commit d6f45c811a #5763: 'Map: Bigred change south lambda padlock and turned it into a checkpoint.' by Huffie56 at commit 646c47711a #5829: 'Event borers' by realforest2001 at commit dee964dd25 #5950: 'Med Skill Rebalance Mk2 Demon Free Edition' by Katskan at commit 9f4b9db6bb #5006: 'Project ARES: Added Tech Unlock logs' by realforest2001 at commit c0645ab04c #5401: 'M540-A Armored Recon Carrier' by Zonespace27 at commit 9be4807644 #5925: 'Biosuit Updates' by realforest2001 at commit bf9853d96c #5946: 'Autocompressor Efficiency Increase' by Katskan at commit 93e4247706

### Round ID

21360

### Description of the bug

Hacking a Rec-Vend and switching between Products and Contraband tabs duplicates the entry for pens. They show up in both tabs and purchasing them does not reduce the listed stock -- they always show as having 10 left. Closing the vendor window resets this.


I then disabled the ID scanner to try buying a bunch, and started getting a "The Rec-Vend beeps, "Sold out of data."" message.

### What's the difference with what should have happened?

Less pens, presumably.

### How do we reproduce this bug?

1. Screwdriver Rec-Vend
2. Pulse Inventory Control
3. Switch tabs
4. Switch tabs again
5. Disrupt the BIC monopoly

### Issue Bingo

- [X] Issue could be reproduced at least once
- [X] Issue happened in a recent (less than 7 days ago) round
- [X] Couldn't find an existing issue about this (https://github.com/cmss13-devs/cmss13/issues)

Start by reproducing the Rec-Vend steps: screwdriver it, pulse Inventory Control, and switch between Products and Contraband. Trace the tab refresh and purchase behavior; done means pens appear in only the correct tab, purchases reduce the listed stock, and reopening the vendor does not merely reset the symptom.

Written by the indexing model from the issue text.