Keep updating while the furnace is low on energy and has educts

The check previously checked for a non zero energy value.
This works when the value only ever decreases by one,
which forces the value to reach zero via reduction.
With the addition of a modifier for cooking cost this breaks down.

This bug was introduced due to the addition of a modifier which
controls the running cost.

sparkfurnace/metalfurnace.lua

@@ -37,7 +37,7 @@ end
 
 local function ongetitem(pos)
 	local meta = minetest.get_meta(pos)
-	if meta:get_int("energy") == 0 then return end
+	if meta:get_int("energy") < modifier then return end
 	local timer = minetest.get_node_timer(pos)
 	timer:start(1.0)
 end
@@ -74,39 +74,38 @@ local function mytime(pos, elapsed)
 	local inventory = meta:get_inventory()
 	local source = inventory:get_list("source")
 	local product = inventory:get_list("product")
-	local counter = 0
-	local newcycle = true -- set to false if not new cycle is required
-  
+
 	for item=1,2 do
-		if energy == 0 then return end --if no energy is available return, rest of the function doesnt matter
-		local cooked
-		local aftercooked
-		local progress = meta:get_int("progress_" .. item)	
-		cooked, aftercooked = minetest.get_craft_result({method = "cooking", width = 1, items = {inventory:get_stack("source", item)}})
-		--source and product assigned
-		if progress >= math.ceil(cooked.time * time_modifier) then
-			if inventory:room_for_item("product", cooked.item) then
-				inventory:add_item("product", cooked.item)
-				inventory:set_stack("source", item, aftercooked.items[1])
-				meta:set_int("progress_" .. item, 0)
+		if energy >= modifier then
+			local cooked
+			local aftercooked
+			local progress = meta:get_int("progress_" .. item)
+			cooked, aftercooked = minetest.get_craft_result({method = "cooking", width = 1, items = {inventory:get_stack("source", item)}})
+			--source and product assigned
+			if progress >= math.ceil(cooked.time * time_modifier) then
+				if inventory:room_for_item("product", cooked.item) then
+					inventory:add_item("product", cooked.item)
+					inventory:set_stack("source", item, aftercooked.items[1])
+					meta:set_int("progress_" .. item, 0)
+				end
 			else
-				counter = counter +1
+				meta:set_int("progress_" .. item, progress + 1)
+				energy = energy - modifier
 			end
-		else
-			meta:set_int("progress_" .. item, progress + 1)
-			energy = energy - 1 * modifier
-			meta:set_int("energy", energy)
+			-- minetest.debug(dump(pos) .. " : " .. dump(item))
 		end
-		-- minetest.debug(dump(pos) .. " : " .. dump(item))
 	end
 
+	meta:set_int("energy", energy)
+	
 	update_formspec(pos) -- Later this should only be done when a player looks into the block
 	
-	if counter == 2 then
-		newcycle = false -- this meens that both finished cooking and the other inventory is full
-	end
 	--TODO: for the formspec code, if it is marked as active update it here
-	if (newcycle) then
+	local has_items = false -- Keep updating if there are still items
+	for _, e in pairs(meta:get_inventory():get_list("source")) do
+		has_items = has_items or not e:is_empty()
+	end
+	if has_items then
 		minetest.get_node_timer(pos):start(1.0) -- it was determined that a new cycle is required, this is the case if energy and material to cook is available
 	end
 	return