message: fix BP3 GetSubFileInfo() step handling which is exclusively used by InSituMPI. Fixes broken InSituMPI tests.
diff: @@ -989,13 +989,14 @@ BP3Deserializer::GetSubFileInfo(const core::Variable<T> &variable) const
  const auto &buffer = m_Metadata.m_Buffer;
  - const size_t stepStart = variable.m_StepsStart + 1;
  - const size_t stepEnd = stepStart + variable.m_StepsCount; // exclusive
  + auto itStep = variable.m_AvailableStepBlockIndexOffsets.begin();
  + const size_t absStepStart = itStep->first; // absolute step in map
  + const size_t stepEnd = absStepStart + variable.m_StepsCount; // exclusive
  const Box<Dims> selectionBox = helper::StartEndBox(
  variable.m_Start, variable.m_Count, m_ReverseDimensions);
  - for (size_t step = stepStart; step < stepEnd; ++step)
  + for (size_t step = absStepStart; step < stepEnd; ++step)
  {
  auto itBlockStarts =
  variable.m_AvailableStepBlockIndexOffsets.find(step);
  