Luca Guadagnino’s “Challengers,” from Amazon MGM Studios, has been showing some decent legs at the box-office. It held strong at No. 3 in its third weekend, only dipping 38 percent to an estimated $4.7 million for a domestic total of $40 million through Monday. It’s so far made $68.7 million globally off a $50 million budget. And yet, it’ll be made available on VOD this coming Friday. Go figure.