FORT WORTH, Texas — Former Dallas Cowboys running back Marion Barber III died from heat stroke last month. The Collin County medical examiner’s office released the findings Monday, calling his death accidental. Barber was found dead inside his Frisco apartment on June 1 by police who were making a welfare check. He was 38. According to the autopsy report, a bathtub faucet in Barber’s apartment was running when officers arrived and the unit’s thermostat was set to 91 degrees with the heat set to “on.” “Mr. Barber was known to exercise in sauna-like conditions,” the coroner wrote in his report. …