Furnace accepts illegal blocks in fuel slot

[Rodarg]

Client version: 1.12.x
Server OS: Windows
Cuberite Commit id: 1edc6c8

Expected behavior

Being unable to put cobblestone in the fuel slot of the furnace

Actual behavior

Furnace accepts cobblestone in fuel slot of furnace

Steps to reproduce the behavior

Place a furnace and put a cobblestone block in fuel slot

[InfRandomness]

I am taking a shot at solving this issue

[supopurskola]

And does the furnace burn it?

[Rodarg]

And does the furnace burn it?

It does not, but it should be impossible to put an invalid block into the slot.