Ender Dragon Frozen After Updating From 1.8 to 1.9

I began the end dragon fight in 1.8.9. I died, re-spawned in the overworld, then only re-entered The End after updating to 1.9. Now the End Dragon is stuck in one place, roaring, and pointing towards an End Crystal that doesn't appear to exist, without being able to take damage. How do I kill it and get out of there?!