Fix flammable item entities crashing (#2659)

mods/default/item_entity.lua

@@ -15,8 +15,8 @@ local item = {
 
 	burn_up = function(self)
 		-- disappear in a smoke puff
-		self.object:remove()
 		local p = self.object:get_pos()
+		self.object:remove()
 		minetest.sound_play("default_item_smoke", {
 			pos = p,
 			max_hear_distance = 8,
@@ -43,12 +43,16 @@ local item = {
 		builtin_item.on_step(self, dtime, ...)
 
 		if self.flammable then
-			-- flammable, check for igniters
+			-- flammable, check for igniters every 10 s
 			self.ignite_timer = (self.ignite_timer or 0) + dtime
 			if self.ignite_timer > 10 then
 				self.ignite_timer = 0
 
-				local node = minetest.get_node_or_nil(self.object:get_pos())
+				local pos = self.object:get_pos()
+				if pos == nil then
+					return -- object already deleted
+				end
+				local node = minetest.get_node_or_nil(pos)
 				if not node then
 					return
 				end