CC0, on the decompilation of a copyrighted work? That's... Not the way it works.

You inherit the copyright from the original, as this is derivative.

There's a reason decompilation has always been a grey area of seeing whether or not the copyright holder cares.

You also get to add your own copyright since decompilation is also a creative enough process. There can be more than one copyright holder in a work.

The main reason you'd avoid this is to stop the first copyright holder from wanting to sue you - not because it's actually invalid.