First drop weedkiller doesn't apply to upper z-levels

## Testmerges
#9894: 'Multiz indicator' by Detective-Google at commit a1fd9677a0
#9978: 'Xeno Time Checks' by realforest2001 at commit f86f8e3705
#9872: ' Multiz Bigred [MDB IGNORE]' by spartanbobby at commit cd86d53c29
#9861: 'M10 revamp, new attachments & additions.' by Zenith00000 at commit e1c802a2cc
#9405: '[EVENT] Pathogen Confluence' by realforest2001 at commit aa797ef03e
#7023: 'Research Rework Part Two: The Contract System.' by kiVts at commit ea3b82d9ab
#10297: 'Adds (very basic) Zombie Hostile Mobs' by Steelpoint at commit bce8fea083

## Round ID
29343

## Description of the bug
The weedkiller dispersed when marines drop doesn't apply to any upper levels of buildings, only the level the Alamo lands at.

## What's the difference with what should have happened?
Weedkiller would apply to all levels of buildings instead of only one.

## How do we reproduce this bug?
1) Disperse weedkiller on Multi-z Solaris
2) Upper levels of buildings covered by weedkiller do not have their weeds killed

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

## Additional details
- Author: Goodwheatley
- Admin: Vending Machine
- Note: None