By GARY GRAFFOf The Oakland PressGary Graff on Music; @graffonmusicJohnny Rzeznik is a happy guy these days, and not just because “Magnetic,” the Goo Goo Dolls’ latest album, debuted at No. 8 on the Billboard 200 chart earlier this month.But with Rzeznik getting ready to remarry and bassist Robby Takac expecting his first child during the recording of the album, there was little reason to delve into the more introspective, heart-rending fare that’s marked much of the Buffalo trio’s other work.“I just wanted to have fun making a record without a lot of pressure,” explains Rzeznik, 47. “The head