Late August can be a depressing time at the movie theater, but there’s a gem to be found in the British romantic comedy “Finding Emily,” which opens in theaters Friday. Here, finally, is a smart, funny and sweet story about young love that moviegoing audiences deserve. Yes, the setup is contrived — it even fits almost entirely into a movie trailer — but it’s in a way that’s familiar and grounded enough, and unlike the insanely dystopian “One Night Only.” There are no ridiculous laws against premarital sex on this university campus in Manchester; Just regular young people getting in their own way.The movie begins with one of those too-good-to-be-true meet cutes, where Owen (Spike Fearn) finds his dream girl (Sadie Soverall) who is dressed in a fairy costume and seems to be into him. Brit pop plays in the background and the world seems to fade away. The night takes her elsewhere with her friends, but not before she gives her number to Owen. He leaves on cloud nine, wondering how much time to let pass before he texts. But there’s a problem: The number is one digit short. Was it intentional? Was it a mistake? He chooses to believe the latter and sets off to find her, knowing only her first name, Emily.