PHILADELPHIA — The 76ers had another unimpressive performance, and, surprisingly, another loss. Saturday’s game against the tanking San Antonio Spurs was supposed to be a breather after opening the season with losses to the Boston Celtics and Milwaukee Bucks. Instead, the Sixers had their hands full and lost, 114-105, Saturday night at the Wells Fargo Center. “We’re not ready yet, honestly,” Doc Rivers said. “We’re just not. We’re not ready to win yet. You can feel that. We got a lot of work to do.” Joel Embiid had his best performance of the season, finishing with 40 points and 13 rebounds. T…