message: Fix explain for VECTOR_SIZE=2
diff: @@ -17,12 +17,17 @@ unique_ptr<PhysicalOperator> PhysicalPlanGenerator::CreatePlan(LogicalExplain &o
  vector<string> values = {op.logical_plan_unopt, logical_plan_opt, op.physical_plan};
  // create a ChunkCollection from the output
  auto collection = make_unique<ChunkCollection>();
  +
  DataChunk chunk;
  chunk.Initialize(op.types);
  - chunk.SetCardinality(keys.size());
  for (index_t i = 0; i < keys.size(); i++) {
  - chunk.SetValue(0, i, Value(keys[i]));
  - chunk.SetValue(1, i, Value(values[i]));
  + chunk.SetValue(0, chunk.size(), Value(keys[i]));
  + chunk.SetValue(1, chunk.size(), Value(values[i]));
  + chunk.SetCardinality(chunk.size() + 1);
  + if (chunk.size() == STANDARD_VECTOR_SIZE) {
  + collection->Append(chunk);
  + chunk.Reset();
  + }
  }
  collection->Append(chunk);
  