SAN DIEGO—If Novak Djokovic wins the U.S. Open two weeks from now to complete the first calendar-year Grand Slam in men’s tennis since 1969, “Rocket” Rod Laver will be there to welcome him into a remarkably exclusive group. “I’d be very happy to shake his hand if he can win the four Slams. I’d be happy for him to be a part of—whether it’s a ‘club’ or not, I don’t know,” Laver said with a chuckle during a recent interview with The Associated Press. No man has won the Australian Open, French Open, Wimbledon, and U.S. Open in the same season since the slightly built, red-haired, left-handed Australian did it for the second time—yes, second—52 years ago. That was so long ago that the Beatles were just about to release “Abbey Road,” and America was still reveling in Neil Armstrong’s moonwalk. The decades have rolled along, and Laver—who also completed a true …