don't call getOutputString when we are not using the result, tdf#92802

Change-Id: I5569eb618b5577714bd10c77ade198638394df8b
Reviewed-on: https://gerrit.libreoffice.org/20725Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

sc/source/filter/xml/xmlcelli.cxx

@@ -1331,7 +1331,7 @@ void ScXMLTableRowCellContext::AddNonFormulaCell( const ScAddress& rCellPos )
 
     if( nCellType == util::NumberFormat::TEXT )
     {
-        if( cellExists(rCellPos) && CellsAreRepeated() )
+        if( !bIsEmpty && !maStringValue && !mbEditEngineHasText && cellExists(rCellPos) && CellsAreRepeated() )
             pOUText.reset( getOutputString(rXMLImport.GetDocument(), rCellPos) );
 
         if (!mbEditEngineHasText && !pOUText && !maStringValue)