In a cramped theater, at the emotional climax of Lulu Wang’s (“Posthumous”) “The Farewell,” an entire row bursts into laughter. Those on the aisle and a family sitting below the main speaker join in, too. This was not the first moment in the film when the laughter of the audience was divided. It was as if the theater were a game of Battleship — the board scattered with red hits and white misses. That was the key to deciphering the uneven responses: the white misses.