Material preview fix for Volumetric scattering mats

For small / thin materials like drinks glasses, vases, glass beads, jewelry, etc. the material previews with volumetric scatting appear much too dark using required distance values for final rendering.

See attached image. In this case 3000mm is a ridiculously large value to get an approximate idea of what this material will look like.

This issue effectively makes the preview for materials with even the smallest amount of vol scattering completely useless.