Clean itemname before checking existence (#234)

important when the item string contains metadata

api.lua

@@ -12,8 +12,9 @@ local function is_recipe_craftable(recipe)
 			end
 		else
 			-- Possibly an item
-			if not minetest.registered_items[itemname]
-					or minetest.get_item_group(itemname, "not_in_craft_guide") ~= 0 then
+			local itemname_cleaned = ItemStack(itemname):get_name()
+			if not minetest.registered_items[itemname_cleaned]
+					or minetest.get_item_group(itemname_cleaned, "not_in_craft_guide") ~= 0 then
 				return false
 			end
 		end