[BLOCKING LIVE CONTENT] Mutant Battle Arena hard crashes on first mob in rush mode.

Verification builds: Release 1064482 - 1.6.0.8 BETA
Summary: Starting Rush Mode in Mutant Battle Arena hard crashes the game.

Repro Steps:

1. Download Mutant Battle Arena
2. run straight into rush mode
3. press level 1

Observed Results: As soon as the dialogue is over, the game will attempt to spawn a zombie_villager at coordinates -47 69 -60. The game crashes immediately. It might have something to do with the is_biome fix because it doesn't happen in other biomes outside of the arena and only in biomes according to the behavior pack like ocean and plains. If you summon one in desert nothing bad happens.

Expected Results: The zombie villager should spawn fine like all the other mobs with the same is_biome detection.

Impact: This renders Mutant Battle Arena unplayable in 4 of the 5 game modes.

Regression Build: 1.5 (all versions) is_biome was only fixed in Beta 18 so I was unable to test this until this build.

Video: https://youtu.be/CPs64eoudQA