Long before the public meltdown became a reliable vehicle for celebrities seeking renewed attention and sympathy, there was one Oscar Levant, who made his name as a brilliant pianist but became almost as well known for his acerbic, sometimes controversial wit and, later, his psychological struggles. Those facets were all on display during a 1958 appearance on “The Tonight Show,” during which Levant, shooting the breeze with host Jack Paar, discussed his depression, chemical addictions, and even the electroshock treatments he endured.