Fix crucible crashing the server.
Crucible should avoid to attempt to add metal to the alloy if the ore is non-smeltable.
Fixes #297.
Fix crucible item disappearing and duping.
Item picked back up from a slot of the crucible had stackSize 0 due to wrong decrStackSize implementation.
When the crucible is broken we have to delete the items it contains otherwise they'll drop and will be a dupe of the one saved in the crucible NBT.
Fixes #296.
Fix StackOverflow when the leaves decay.
Code to avoid this was already in place, but we have to avoid to trigger the block update when setting the current leaf block to air.