Revert "[ntuple] Simplify vector construction in friend page source"

This reverts commit a9ef733.

Author: jblomer

tree/ntuple/v7/src/RPageSourceFriends.cxx

@@ -203,5 +203,8 @@ ROOT::Experimental::Detail::RPageSourceFriends::LoadClusters(std::span<RCluster:
 {
    // The virtual friends page source does not pre-load any clusters itself. However, the underlying page sources
    // that are combined may well do it.
-   return std::vector<std::unique_ptr<ROOT::Experimental::Detail::RCluster>>(clusterKeys.size(), nullptr);
+   std::vector<std::unique_ptr<ROOT::Experimental::Detail::RCluster>> result;
+   for (unsigned i = 0; i < clusterKeys.size(); ++i)
+      result.push_back(nullptr);
+   return result;
 }