fermenter: improve input items processing.

Change source item pulling logic: previously 2 leaves items
were taken at once from the same stack, so only identical types
were used to produce Biogas (remaining single items could fill
up source tray). Now items are taken one by one, allowing 2
different plant leaves to form 1 Biogas unit. That cleans up
inventory as well - maximum one item is left there when production
ends.

Signed-off-by: Michal Cieslakiewicz <michal.cieslakiewicz@wp.pl>

tubelib_addons1/fermenter.lua

@@ -91,18 +91,32 @@ local function convert_leaves_to_biogas(meta)
 	local inv = meta:get_inventory()
 	local biogas = ItemStack("tubelib_addons1:biogas")
 	if inv:room_for_item("dst", biogas) then					-- enough output space?
-		local items = tubelib.get_num_items(meta, "src", 2)
+		local items = {}
-		if items then											-- input available?
+		local fault = false
-			if is_leaves(items:get_name()) then
+		for i = 1, 2 do
+			items[i] = tubelib.get_num_items(meta, "src", 1)
+			if items[i] then						-- input available?
+				if not is_leaves(items[i]:get_name()) then
+					fault = true
+					break
+				end
+			else
+				break
+			end
+		end
+		if #items == 2 then
 			inv:add_item("dst", biogas)
 			return true
 		else
-				inv:add_item("src", items)
+			for i = 1, #items do
-				return nil  -- error
+				inv:add_item("src", items[i])
 			end
+			if fault then
+				return nil  -- error
 			else
 				return false  -- standby
 			end
+		end
 	else
 		return false  -- standby
 	end