Currently ogt_vox.h will assert on loading a model with 0 size when reading the CHUNK_ID_XYZI at line:

1320 ogt_assert(size_x && size_y && size_z, "expected a SIZE chunk before XYZI chunk");

https://github.com/jpaver/opengametools/blob/master/src/ogt_vox.h#L1320

This can be a little confusing, as the actual error can be due to the model having zero size. In addition I discovered this by saving out a .vox file with a model of zero size, so here I have also added an assert for this case in the write code.

Whilst MV appears to handle loading a 0 size model you can't create one using it's UI, so it's likely still good practice to assert on this.