New York — On a quiet weekend in movie theaters, while much of Hollywood’s attention was on the wildfires that continue to rage in Los Angeles, Lionsgate’s “Den of Thieves 2: Pantera” debuted atop the box office with $15.5 million, according to studio estimates Sunday. Mid-January is often a slow moviegoing period, and that was slightly exacerbated by the closures of about 10 theaters in Los Angeles, the country’s top box-office market. A sequel to the Gerard Butler 2018 heist thriller, “Den of Thieves 2” performed similarly to the original. The first installment, released by STX, opened with $15.2 million