The piranhas of the New York press proved to be a cold fish audience at a preview of Bette Midler’s “Clams on the Half Shell Revue.” It was a crowd that I would not care to face if I were hitting the stage of the Minskoff Theatre with a “comeback” at stake. There was no rushing the stage, no anticipatory laughter, none of that audience sweetening on which Midler’s particular act has always depended.