Enabling "grid" option affecting depth test

[donmccurdy]

Testing this model: https://sketchfab.com/3d-models/low-poly-car-chevrolet-c10-pickup-1963-679354c151984747bb74310ec5af8995#download

If I enable/disable the grid, depth information is being lost and some backfaces show through the front of the vehicle. Possibly related to this line:

three-gltf-viewer/src/viewer.js

Line 510 in d428e8f

this.axesHelper.onBeforeRender = (renderer) => renderer.clearDepth();