message: Fix LoadCachedIndex crash if deserialization failed.
diff: @@ -33,6 +33,7 @@ std::unique_ptr<IndexFile> LoadCachedIndex(Config* config,
  return nullptr;
  auto result = Deserialize(filename, *file_content, IndexFile::kCurrentVersion);
  + if (result)
  result->is_loaded_from_cache_ = true;
  return result;
  }
  