Hybrisa Prospera - Larva able to spawn ontop of invisible wall.

### Testmerges

N/A

### Round ID

N/A

### Description of the bug

Location of 91,59,2

This is an open turf that just has an invisible wall ontop of it.

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

Larvas shouldn't spawn off weeds, in a "wall" out of bounds.

### How do we reproduce this bug?

1. Roll LV-759
2. Get lucky enough to spawn into an invisible wall apparently.
3. Cry
...

### 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)