Fixed gases deleting all overlays of a turf when spreading.

Better code

SHIT

code/LINDA/LINDA_turf_tile.dm

@@ -232,15 +232,13 @@
 	archived_cycle = SSair.times_fired
 
 /turf/simulated/proc/update_visuals(datum/gas_mixture/model)
-	overlays.Cut()
-	var/siding_icon_state = return_siding_icon_state()
-	if(siding_icon_state)
-		overlays += image('icons/turf/floors.dmi',siding_icon_state)
+	overlays -= SSair.plasma_overlay
+	overlays -= SSair.sleeptoxin_overlay
 	switch(model.graphic)
 		if("plasma")
-			overlays.Add(SSair.plasma_overlay)
+			overlays += SSair.plasma_overlay
 		if("sleeping_agent")
-			overlays.Add(SSair.sleeptoxin_overlay)
+			overlays += SSair.sleeptoxin_overlay
 
 /turf/simulated/proc/share_air(var/turf/simulated/T)
 	if(T.current_cycle < current_cycle)

code/game/turfs/turf.dm

@@ -107,8 +107,6 @@
 
 /turf/proc/is_plasteel_floor()
 	return 0
-/turf/proc/return_siding_icon_state()		//used for grass floors, which have siding.
-	return 0
 
 /turf/proc/levelupdate()
 	for(var/obj/O in src)