Skip drawing zero-length VAOs, fixes "Render count or primcount is 0."
Skip drawing zero-length VAOs, fixes "Render count or primcount is 0."

Chrome now warns when drawing zero-length:

16localhost/:1 [.CommandBufferContext]RENDER WARNING: Render count or primcount is 0.

Closes https://github.com/deathcap/voxelmetaverse/issues/109

voxel/voxel-shader