improved packet rate for conveyor belts

since by default the belt renders down there is no point in sending a
packet to tell the client its already rendering correctly. This should
save on lag spikes when logging into rooms full or conveyor belts
Fixed create loading items that don't exist

Since the create saves item stacks different than MC it would load them
even if the item they went too no longer existed. I'll work on a more
improved fix for this that will save the unlocalized name so in case the
IDs change the create remembers what was in it.