By Daniel Chavkin No, those smiling fans weren’t natural. If you were watching a baseball game last night, you might’ve noticed someone behind home plate who couldn’t stop smiling in a very creepy fashion. As it turns out, that was not a coincidence. The two fans who attended the Red Sox-Yankees, Mets-Athletics and Cardinals-Dodgers games on Friday night were actors promoting Smile, a horror movie that apparently features villains with a bunch of very creepy smiles. It was certainly impressive that these actors were able to hold their smiles for the entire game, and the marketing definitely wo…