Emplace scalar tuple only when needed

Author: franzpoeschel

include/openPMD/backend/BaseRecord.hpp

@@ -28,6 +28,7 @@
 #include "openPMD/backend/Container.hpp"
 
 #include <array>
+#include <optional>
 #include <stdexcept>
 #include <string>
 #include <type_traits> // std::remove_reference_t
@@ -114,9 +115,7 @@ namespace internal
         {}
         ScalarIterator(T_BaseRecord *baseRecord, Left iterator)
             : m_baseRecordData(&baseRecord->get())
-            , m_scalarTuple(
-                  std::make_pair(
-                      RecordComponent::SCALAR, T_RecordComponent(*baseRecord)))
+            , m_scalarTuple(std::nullopt)
             , m_iterator(std::move(iterator))
         {}