10 years after his TED Talk, Dan Pallotta is back with “An Inconvenient Truth” for charities. The fundraiser and activist’s new film UnCharitable, a polemical adaptation of Pallotta’s 2008 book of the same name, once again takes aim at the so-called overhead myth, the dogma that nonprofits ought to be rewarded for minimizing their overhead costs, even for essentials like salaries, rent, or insurance.