message: fix: bugs in StringIndex
  by chenjiaqi
diff: @@ -108,6 +108,9 @@ void StringIndexFile::addRequest(unsigned id, std::string *str)
  void StringIndexFile::trySequenceAccess()
  {
  + if (this->request.empty())
  + return;
  +
  long min_begin = -1, max_end = 0;
  for (int i = 0; i < (int)this->request.size(); i++)
  {
  @@ -156,6 +159,9 @@ void StringIndexFile::trySequenceAccess()
  long offset = this->request[pos].offset;
  long length = this->request[pos].length;
  + if (offset >= current_block_end)
  + break;
  +
  if (current_block_begin <= offset && offset + length <= current_block_end)
  {
  allocBuffer(length);
  