message: Fix for undo buffer
diff: @@ -21,13 +21,15 @@ static void CleanupIndexInsert(VersionInfo *info);
  static void RollbackIndexInsert(VersionInfo *info);
  UndoBuffer::UndoBuffer() {
  - head = make_unique<UndoChunk>(DEFAULT_UNDO_CHUNK_SIZE);
  + head = make_unique<UndoChunk>(0);
  tail = head.get();
  }
  UndoChunk::UndoChunk(index_t size) : current_position(0), maximum_size(size), prev(nullptr) {
  + if (size > 0) {
  data = unique_ptr<data_t[]>(new data_t[maximum_size]);
  }
  +}
  UndoChunk::~UndoChunk() {
  if (next) {
  auto current_next = move(next);
  @@ -394,7 +396,7 @@ void CommitState::WriteInsert(VersionInfo *info) {
  }
  bool UndoBuffer::ChangesMade() {
  - return entries.size() > 0;
  + return head->maximum_size > 0;
  }
  template <bool HAS_LOG> void CommitState::CommitEntry(UndoFlags type, data_ptr_t data) {
  