Blender Git Loki

Fix T65996: metaballs converted to meshes appear to render at an incorrect isosurface.

Not much to be done here really, besides adding yet another hack to that
giant pile of hacks that are mballs...

So to avoid newly created copy of basis of mball to influence to mball
computation, we simply switch it to Empty object for the depsgraph
update run.

Not nice, but working (besides a weird change of basis obflag which
should not happen), and presumably reasonably safe change.