During a raucous Democratic Party fundraiser Thursday night at Dream, the hot dance club in Northeast Washington, deejay Biz Markie kept promising the young, well-lubricated crowd that Sean ‘P. Diddy’ Combs and Leonardo DiCaprio were in the house as part of the festivities with rapper Q-Tip, ‘The View’s’ Star Jones, Al Sharpton, Hillary Rodham Clinton and the biggest names of all: former presidents Bill Clinton and Jimmy Carter. But neither Puffy nor Leo showed up. Turns out Leo was never scheduled to appear, his spokesman told us. And though the Democratic National Committee had hoped to score an appearance by Diddy, he couldn’t break away from rehearsals for his Broadway debut.