Director Stephen Gaghan is spilling details on what went through his mind when colleague Heath Ledger was found dead in 2008. While appearing on the “Developmental H—” podcast, Gaghan talked to Blink author Malcolm Gladwell about how he was in the process of turning his book into a movie. At first, the Oscar-winning filmmaker, 58, had been discussing the possible film with Leonardo DiCaprio, 49, but after crossing paths with the late father-of-one — who passed away at age 28 due to an accidental drug overdose — he knew Ledger was the right one for the lead role. “I had met Heath Ledger and I…