MIAMI – Once again, the defending champion Miami Heat – the favorites to win the title again this season, winners of 18 consecutive games, owners of best record in the NBA, darlings of media and fans alike – find themselves walking a high wire without a safety net. Almost everybody expects the Heat, led by superstars LeBron James and Dwyane Wade, to repeat as champions. They look unbeatable in a best-of-seven series. Heck, they look unbeatable every night, something they’ve been