Furnaces with smelted items in the output slot don't give experience or recipes after upgrading from 1.12.2

To reproduce:

1. Smelt something in 1.12.2, but don't take it out of the furnace
2. Open the world in 18w08b
3. /recipe take @a *
4. Take the smelted items out of the furnace
5. Observe that you didn't get any experience and no recipe was rewarded