It was the tale of two stars at the weekend box office, one who opened a film — Jennifer Lopez with Universal’s The Boy Next Door at $15M — and one who tanked — Johnny Depp with Lionsgate’s Mortdecai at $4.1M. The discrepancy between the two films showed one star, Lopez, who kept it cheap and met her audience's wants head-on, and another, Depp, who at a high price lost himself in a zany caricature disconnected from reality. Universal's Blumhouse production Boy Next Door…