Fix: zero interior band width leads to no volume output

The input only determines the gradient of the volume density at its surface.
Using zero there should not break it.

Pull Request: https://projects.blender.org/blender/blender/pulls/109208

source/blender/geometry/intern/mesh_to_volume.cc

@@ -111,7 +111,7 @@ static openvdb::FloatGrid::Ptr mesh_to_fog_volume_grid(
     const float interior_band_width,
     const float density)
 {
-  if (voxel_size < 1e-5f || interior_band_width <= 0.0f) {
+  if (voxel_size < 1e-5f) {
     return nullptr;
   }