Arlington Park Racecourse is not liable for a jockey’s paralyzing back injury during a horse race, a Cook County jury has found.The verdict came earlier this month in a lawsuit brought by plaintiffs Rene and Natalia Douglas, who alleged the Arlington Heights track and its owner, Churchill Downs Inc., installed an unreasonably dangerous racetrack that caused Rene Douglas to severely injure his back and become paralyzed when he fell off of his horse during a race.The facility’s main racetrack was a dirt surface …