Katie Price is a 17-year-old girl who lives with a life-threatening sensitivity to sunlight. “Midnight Sun” does what it means to do for the people it means to do it for—and that might just be enough. The 12-year-old girls who are the film’s target audience probably won’t realize what it’s derivative of: a little bit of John Hughes and a lot of “Love Story.” “Midnight Sun” also bears more than a slight resemblance to last summer’s Young Adult drama “Everything, Everything,” in which a rare disease supposedly spells doom for a blossoming teen romance. (Director Scott Speer’s film is actually based on a 2006 Japanese film of the same name.) Xeroderma pigmentosum—a one-in-a-million skin ailment that makes exposure to the sun’s rays potentially deadly—wouldn’t necessarily sound like the sexiest starting point for a life-changing love. But “Midnight Sun” has the benefit of photogenic, charismatic co-stars in Bella Thorne and Patrick Schwarzenegger, who have enough likability and chemistry to make this high school weepy more tolerable than it ought to be—for a while, at least, until it goes off the rails and turns unbearably schmaltzy in the third act.