By Robert Baird Wednesday, May 15 1991"I don't know, I guess I'm just missing my girlfriend today," says Johnny Rzeznik. Talking by telephone from a tour stop in Cleveland, the guitarist and singer for Goo Goo Dolls sounds wrung out and depressed. "All three of us are in a weird mood today. We all miss our girlfriends."Miss their girlfriends? Are these the same sneering punks who've shattered eardrums and spat on adoring fans from Tonawanda to Topanga and back?What in the name of Husker Du is going on? Has one of America's finest power trios lost its guts? Or is it the creeping influence of th