LOS ANGELES — “Glee” star Naya Rivera died of accidental drowning, the Ventura County medical examiner said on Tuesday, marking the third tragic passing of a cast member from the popular television musical series.Rivera, 33, was found in Lake Piru, near Los Angeles, on Monday, five days after going missing on a boating trip with her young son.The medical examiner’s report said there was no indication that drugs or alcohol played a role in her death and no traumatic injuries or other medical