When Johnny Rzeznik and Robby Takac started the Goo Goo Dolls they figured that they’d have some fun for a year, year-and-a-half at most, then the band, like most garage rock outfits, would flame out and they’d be onto something new.Thirty-one years later, the Goo Goo Dolls are still together and going strong -- and Rzeznik, 51, is at a loss to explain how or why.“I don’t know,” he said in a telephone interview from his New Jersey home. “It’s a lot of luck, a good manager and this kind of dogged determination to not give up. And it’s a question of having limited options. Robby and I don’t real