message: fix bug in json_scan
diff: @@ -235,8 +235,10 @@ void JSONScanLocalState::ReadNextBufferSeek(JSONScanGlobalState &gstate, bool &f
  break; // No more files left
  }
  }
  - D_ASSERT(read_size != 0);
  buffer_size = prev_buffer_remainder + read_size;
  + if (buffer_size == 0) {
  + return;
  + }
  // Now read the file lock-free!
  auto &file_handle = gstate.json_reader->GetFileHandle(file_index);
  @@ -273,7 +275,6 @@ void JSONScanLocalState::ReadNextBufferNoSeek(JSONScanGlobalState &gstate, bool
  break; // No more files left
  }
  }
  - D_ASSERT(read_size != 0);
  buffer_size = prev_buffer_remainder + read_size;
  }
  