The Knicks — and all of their fans — can breathe again. Kristaps Porzingis was diagnosed with a sprained right ankle after X-rays were negative Wednesday night, the team announced, which must be considered the best-case scenario after the future of the franchise had limped off the court following what appeared to be a nasty injury. The play happened with about 9:40 on the clock in the first quarter against the Heat as Porzingis was trying to chase down a rebound. The Heat’s Justise Winslow stepped on Porzingis’ right foot, and television replays showed Porzingis’ ankle turning all the way over. A hush went over the Garden crowd.