Infinite stacked chair exploit

### Testmerges

#5007, #5392, #5552, #5628

### Round ID

20837

### Description of the bug

Marines and I were stacking chairs in briefing like normal and somehow ended up breaking the chair code, causing it go into the negatives and create infinite chairs.

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

uhhhhh, probably not negative chairs.

### How do we reproduce this bug?

1. I have no earthly idea
2. spam stack chairs, we had like 5 people doing it.
3. profit?

### 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)