Since it gives negative power, how is rcon(0) calculated in AES?
See my previous answer here regarding rcon calculation:

Rijndael: explanation of Rcon on Wikipedia?

It is essentially caulcated by division of 0x01 within the finite field.

The most important thing about rcon(0) is that there is no round 0, and thus you will never actually use it in any calculation. Also take note of my comment that the Wikipedia page is not completely correct. I will probably edit the page if someone else does not get to it first.