Fix bugs with area contents system (#95337)

## About The Pull Request
Contains two changes cherry-picked from my CM PR,
https://github.com/cmss13-devs/cmss13/pull/11826.

1) Fixes incorrect args to `block()` in `increase_max_y()` that caused
it to add turfs to every z-level's world.area contents list instead of
just the correct one. This is probably left over from when the area
contents list wasn't split by z-level.

2) Avoids a case where turfs could be removed from area contents twice
if the subsystem returned early on a later Z-level.

## Why It's Good For The Game
Fixes two bugs with the area contents system.

## Changelog

🆑 MoondancerPony
fix: fixed turfs sometimes not being in any area's contents
/🆑

code/controllers/subsystem/area_contents.dm

@@ -63,6 +63,8 @@ SUBSYSTEM_DEF(area_contents)
 				if(MC_TICK_CHECK)
 					cut_from.Cut(1, amount_cut + 1)
 					return
+			// avoid double removals if we return early on a subsequent z-level
+			clear.turfs_to_uncontain_by_zlevel[area_zlevel] = list()
 
 		clear.turfs_to_uncontain_by_zlevel = list()
 		marked_for_clearing.len--