fix crash during (artificial) village creation

when using the village tool doing that on an unsuitable location
would result in no position for the belltower being available
this checks for that and ... doesn't crash then ^^

mods/MAPGEN/mcl_villages/buildings.lua

@@ -237,18 +237,20 @@ function settlements.place_schematics(settlement_info, pr)
 	
 	--attempt to place one belltower in the center of the village - this doesn't always work out great but it's a lot better than doing it first or last.
 	local belltower = table.remove(settlement_info,math.floor(#settlement_info/2))
-	mcl_structures.place_schematic(
-		vector.offset(belltower["pos"],0,1,0),
-		settlements.modpath.."/schematics/belltower.mts",
-		belltower["rotation"],
-		nil,
-		true,
-		nil,
-		function(p1, p2, size, rotation, pr)
-			spawn_iron_golem(p1)
-		end,
-		pr
-	)
+	if belltower then
+		mcl_structures.place_schematic(
+			vector.offset(belltower["pos"],0,0,0),
+			settlements.modpath.."/schematics/belltower.mts",
+			belltower["rotation"],
+			nil,
+			true,
+			nil,
+			function(p1, p2, size, rotation, pr)
+				spawn_iron_golem(p1)
+			end,
+			pr
+		)
+	end
 	
 	for i, built_house in ipairs(settlement_info) do
 		local is_last = i == #settlement_info