In the past, rom-coms starring Jennifer Lopez often saddled her with professions that are just too unbelievable. “Maid in Manhattan”? “The Wedding Planner”? Not our Jenny from the Block. So it’s refreshing to see J.Lo, in a much-heralded return to the romantic comedy fold, playing a character who just makes sense for her: a global pop superstar. But it’s not just a professional life that Lopez shares with her character, Kat Valdez, in “Marry Me,” directed by Kat Coiro, based on a graphic novel by Bobby Crosby, and that’s a good thing. Lopez brings authenticity to her portrayal of Kat Valdez, a…