LAS VEGAS – There was a time, not all that long ago, when stepping into the cage with striking specialist Mirko Cro Cop Filipovic was considered an awfully risky proposition. But with Filipovic currently mired in 2-3 slump, the aura of invincibility that he once carried into combat no longer exists. Nevertheless, his UFC 137 opponent, Roy Nelson, believes Filipovic is still a worthy opponent. Sure, the losses have damaged the Croatian’s fighting reputation, but Nelson believes it’s still an hono…