message: Fix race condition when computing leafValueRange
diff: @@ -58,7 +58,7 @@ cpp::Group VdbVolume::buildGroup() const
  for (uint32_t z = 0; z < N; ++z)
  for (uint32_t y = 0; y < N; ++y)
  for (uint32_t x = 0; x < N; ++x) {
  - range1f leafValueRange;
  + std::vector<range1f> leafValueRange(leafRes);
  tasking::parallel_for(leafRes, [&](uint32_t vz) {
  for (uint32_t vy = 0; vy < leafRes; ++vy)
  for (uint32_t vx = 0; vx < leafRes; ++vx) {
  @@ -71,12 +71,15 @@ cpp::Group VdbVolume::buildGroup() const
  const size_t idx =
  vx * (size_t)leafRes * leafRes + vy * (size_t)leafRes + vz;
  - leafValueRange.extend(v);
  + leafValueRange[vz].extend(v);
  leaf.at(idx) = v;
  }
  });
  + // reduction
  + for (auto &vr : leafValueRange)
  + leafValueRange[0].extend(vr);
  - if (leafValueRange.lower != 0.f || leafValueRange.upper != 0.f) {
  + if (leafValueRange[0].lower != 0.f || leafValueRange[0].upper != 0.f) {
  level.push_back(3);
  origin.push_back(vec3i(x * leafRes, y * leafRes, z * leafRes));
  data.emplace_back(
  