Joseph Cosina was shot in the heart after bar-close early Friday morning at Crash Mansion nightclub on Grand Ave. (it was an 18-and-over event). The 19-year-old Downey High School graduate was pronounced dead at the hospital and two others were wounded. The gunman remains at large.About closing time, a fight broke out inside the club, police said. Cosina and his friends had no connection to the fight, said his father, Hector. Security guards asked them......