We told you it was a bad idea to underestimate Melinda Katz. The latest WABC poll shows that she has taken the lead in the city comptroller’s race over nearest competitor John Liu, 27 percent to 21 percent. And this time she’s ahead of “Undecided,” too. David Yassky, despite the Times‘ endorsement, gets 18 percent, and David Weprin 11 percent. On the other hand, Liu knew how much the comptroller’s office budget was when the Daily News asked the candidates about it; Yassky sort of knew, and Katz and Weprin could not provide a figuire. The Bond Buyer has a more substantive discussion with the candidates minus Katz. The other races tracked by WABC are more or less status quo.