One man was stabbed and three teen-agers were robbed of their tickets at gunpoint as police called in dog squads and extra officers to end violence Wednesday night outside a San Antonio, Tex., concert by the top-selling group Bon Jovi. “It’s a jungle out there,” Sgt. Billy Hook said of trouble that erupted outside the Convention Center Arena, where a sell-out crowd of 15,000 people gathered. Police said a 21-year-old man was stabbed in the chest before the show by someone allegedly trying to take his tickets. Three teen-agers were robbed of their tickets at gunpoint, said police, who arrested two youths as suspects. Police said no problems were reported inside the arena.