[1.7 BLOCKING] Vex model has holes in upcoming everbloom project.

Verification Builds: 117901

Summary: A custom model for the vex has a number of one pixel holes in one of the wings.

Impact: This makes this model look bad and would hinder the release of this project.

Repro Steps:

1. Make a new world and add a resource pack with the attached mobs.json and vex texture.
2. Summon a vex.

Observed Results: The vex's wing has a number of holes when looked at from the right angle.

Expected Results: The vex's wing appears solid.

Screenshots / Videos Attached: No.

Regression Build: 1.6.0.8