Grindr's CEO says his stock trades at a 25% discount because straight portfolio managers are too uncomfortable pitching a gay hookup app to their investment committee. He might even be right at the margins. But the ownership table hands fund managers a far more boring reason to pass. Two shareholders, Ray Zage and James Lu, control more than 60% of Grindr. Last October they offered $18 a share to take the company private. Then the board's special committee walked away from the deal, citing…