the "remove mindless mobs" option for ERT deletes all mobs in the ERT

## Testmerges
#10999: 'Fix of various plane related issues' by Blundir at commit f85a7153c4
#11661: 'Despoiler rework' by Git-Nivrak at commit c0f8d2884f
#11590: 'Elite Human Hunting Grounds Presets' by dawsonkeyes at commit f154d98543

## Round ID
32643

## Description of the bug
spawning an ERT with "remove mindless mobs" deleted the entire ERT; despite some players readying

## What's the difference with what should have happened?
it shouldve only deleted the ones that overflowed

## How do we reproduce this bug?
1. spawn 15 romans with delete mindless set to yes
2. all of them get deleted
3. confirm in deadchat that players did sign up for it and just didnt get spawned

## Attached logs
```
N/A
```

## Additional details
- Author: detectivegoogle
- Admin: the detectivegoogle
- Note: None