Set is_ground_content to false (#386)

mesecons_movestones/init.lua

@@ -70,6 +70,8 @@ function mesecon.register_movestone(name, def, is_sticky, is_vertical)
 		end
 	end
 
+	def.is_ground_content = false
+
 	def.mesecons = {effector = {
 		action_on = function(pos, node, rulename)
 			if rulename and not minetest.get_node_timer(pos):is_started() then
@@ -90,8 +92,6 @@ function mesecon.register_movestone(name, def, is_sticky, is_vertical)
 
 	def.on_blast = mesecon.on_blastnode
 
-	def.on_blast = mesecon.on_blastnode
-
 	minetest.register_node(name, def)
 end