message: stdtype: format/bp3 fix to use "signed char" for type_byte.
diff: @@ -350,8 +350,8 @@ void BP3Serializer::UpdateOffsetsInMetadata()
  case (type_byte):
  {
  - UpdateIndexOffsetsCharacteristics<char>(currentPosition,
  - type_byte, buffer);
  + UpdateIndexOffsetsCharacteristics<signed char>(
  + currentPosition, type_byte, buffer);
  break;
  }
  @@ -1137,8 +1137,9 @@ void BP3Serializer::MergeSerializeIndices(
  case (type_byte):
  {
  - const auto characteristics = ReadElementIndexCharacteristics<char>(
  - buffer, position, type_byte, true);
  + const auto characteristics =
  + ReadElementIndexCharacteristics<signed char>(buffer, position,
  + type_byte, true);
  count = characteristics.EntryCount;
  length = characteristics.EntryLength;
  timeStep = characteristics.Statistics.Step;
  