message: fix fetch does not get the correct result
diff: @@ -33,7 +33,10 @@ public:
  auto prefix = NebulaKeyUtils::vertexPrefix(planContext_->vIdLen_, partId, vId);
  auto ret = planContext_->env_->kvstore_->prefix(planContext_->spaceId_,
  partId, prefix, &iter);
  - if (ret != kvstore::ResultCode::SUCCEEDED || iter == nullptr || !iter->valid()) {
  + if (ret != kvstore::ResultCode::SUCCEEDED) {
  + return ret;
  + }
  + if (iter == nullptr || !iter->valid()) {
  // not emplace row when vertex not exists
  return kvstore::ResultCode::SUCCEEDED;
  }
  