fdo#75960: No point instantiating the struct when there are no pivot tables.

Just a tiny micro-optimization.

Change-Id: I850bebc63a3f51456326b09ce72442845ea04478

sc/source/filter/xml/xmlimprt.cxx

@@ -3232,7 +3232,9 @@ void SAL_CALL ScXMLImport::endDocument()
             SetLabelRanges();
             SetNamedRanges();
             SetSheetNamedRanges();
-            GetPivotTableSources().process();
+            if (mpPivotSources)
+                // Process pivot table sources after the named ranges have been set.
+                mpPivotSources->process();
         }
         GetProgressBarHelper()->End();  // make room for subsequent SfxProgressBars
         if (pDoc)