Try to fix some bugs that happen on server restart

item_transport.lua

@@ -361,7 +361,8 @@ minetest.register_entity("pipeworks:tubed_item", {
 		initial_sprite_basepos = {x = 0, y = 0},
 		is_visible = false,
 		start_pos = {},
-		route={}
+		route = {},
+		removed = false
 	},
 	
 	itemstring = '',
@@ -399,7 +400,9 @@ minetest.register_entity("pipeworks:tubed_item", {
 	end,
 
 	get_staticdata = function(self)
-		if self.start_pos==nil then return end
+		if self.start_pos == nil or self.removed then
+			return
+		end
 		local velocity = self.object:getvelocity()
 		self.object:setpos(self.start_pos)
 		return	minetest.serialize({
@@ -428,7 +431,16 @@ minetest.register_entity("pipeworks:tubed_item", {
 		self:set_item(item.itemstring)
 	end,
 	
+	remove = function(self)
+		self.object:remove()
+		self.removed = true
+		self.itemstring = ''
+	end,
+
 	on_step = function(self, dtime)
+		if self.removed then
+			return
+		end
 		if self.start_pos == nil then
 			local pos = self.object:getpos()
 			self.start_pos = roundpos(pos)
@@ -481,7 +493,7 @@ minetest.register_entity("pipeworks:tubed_item", {
 				leftover = stack
 			end
 			if leftover:is_empty() then
-				self.object:remove()
+				self:remove()
 				return
 			end
 			velocity.x = -velocity.x
@@ -497,7 +509,7 @@ minetest.register_entity("pipeworks:tubed_item", {
 				drop_pos = minetest.find_node_near(vector.add(self.start_pos, velocity), 1, "air")
 				if drop_pos then 
 					minetest.item_drop(stack, "", drop_pos)
-					self.object:remove()
+					self:remove()
 				end
 			end
 		end