Adds z.7 (dead space 2) to boxstation because no one seemed particularly offended by the idea. This closes the cube properly there and prevents a few weird edge cases where closed loops of Z.6 to Z.6 transitions could happen.

Meta/Mini should add empty z.7 at some point after this pull is committed, I would have done so myself but it didn't play nice with mapmerge so I decided against it.

code/_globalvars/lists/mapping.dm

@@ -12,7 +12,7 @@ var/list/alldirs = list(NORTH, SOUTH, EAST, WEST, NORTHEAST, NORTHWEST, SOUTHEAS
 //Was list("3" = 30, "4" = 70).
 //Spacing should be a reliable method of getting rid of a body -- Urist.
 //Go away Urist, I'm restoring this to the longer list. ~Errorage
-var/list/accessable_z_levels = list(1,3,4,5,6,6)
+var/list/accessable_z_levels = list(1,3,4,5,6,7) //Keep this to six maps, repeating z-levels is ok if needed
 
 var/global/list/global_map = null
 	//list/global_map = list(list(1,5),list(4,3))//an array of map Z levels.

code/game/turfs/space/space.dm

@@ -143,6 +143,8 @@
 			z_level =  6
 		else
 			z_level = pick(unplaced_z_levels)
+		if(z_level >> world.maxz) //A safety if one of the unplaced_z_levels doesn't actually exist
+			z_level =  6
 		placement = pick(free_zones)
 		text_zone_connections = replacetext(text_zone_connections, placement, "[z_level]")