Currently it is always set to the size of the block texture atlas. When an atlas isn't bound, it should be set to (0, 0).

Would #549 not fix this?

It would probably fix it for 1.16 but I don't think it would work on 1.17. Also, it doesn't refer to any atlas texture, but rather the texture bound to texture / gtexture / tex, which could end up being an important distinction in modded environments.