Fix actors being able to walk on cliffs after the sietch was destroyed

mods/d2k/maps/atreides-04/atreides04.lua

@@ -158,6 +158,7 @@ WorldLoaded = function()
 	end)
 
 	Trigger.OnKilled(Sietch, function()
+		Actor.Create("invisibleBlocker", true, { Owner = fremen, Location = CPos.New(62, 59) })
 		UserInterface.SetMissionText("Sietch destroyed!", player.Color)
 		player.MarkFailedObjective(ProtectFremen)
 	end)

mods/d2k/maps/atreides-04/rules.yaml

@@ -88,3 +88,10 @@ tile475:
 	BodyOrientation:
 		QuantizedFacings: 1
 	AutoSelectionSize:
+
+# Placed after the sietch is destroyed so that the cliff is still unpassable
+invisibleBlocker:
+	AlwaysVisible:
+	Building:
+		Footprint: xx xx
+		Dimensions: 2,2