Improperly checked IDs on itemstacks received from the client leading to server crash in PocketMine-MP

Impact Due to a workaround for unmapped network items implemented in 4.0.0-BETA5 8ac16345a3bc099b62c1f5cfbf3b736e621c3f76, arbitrary item IDs are able to be written into an item's NBT. The intended purpose of this is to make said unmapped network items able to be moved around the inventory withou...