How on earth can White Sox right-hander David Sandlin top his major-league debut, in which he retired 18 consecutive hitters after allowing a leadoff home run?‘‘Well, if he doesn’t throw a no-hitter, it might be a failure,’’ Sox pitching coach Zach Bove joked Sunday.A no-no certainly would be an improvement, but not by a lot. Sandlin, a 6-4, 220-pounder with a fastball that reached 97.7 mph in the Sox’ 15-2 drubbing of the Twins on Wednesday, wi…