valgrind: check return of convertDateTime before using fDate

lots of spew in VALGRIND=memcheck make CppunitTest_writerperfect_calc

Change-Id: I8b95e95218beefe19e881c9d055323d0abec49c7

sc/source/filter/xml/xmlcelli.cxx

@@ -935,7 +935,8 @@ void ScXMLTableRowCellContext::SetAnnotation(const ScAddress& rPos)
     if( pNote )
     {
         double fDate;
-        rXMLImport.GetMM100UnitConverter().convertDateTime( fDate, mxAnnotationData->maCreateDate );
+        if (rXMLImport.GetMM100UnitConverter().convertDateTime(fDate, mxAnnotationData->maCreateDate))
+        {
             SvNumberFormatter* pNumForm = pDoc->GetFormatTable();
             sal_uInt32 nfIndex = pNumForm->GetFormatIndex( NF_DATE_SYS_DDMMYYYY, LANGUAGE_SYSTEM );
             OUString aDate;
@@ -943,6 +944,7 @@ void ScXMLTableRowCellContext::SetAnnotation(const ScAddress& rPos)
             Color** ppColor = &pColor;
             pNumForm->GetOutputString( fDate, nfIndex, aDate, ppColor );
             pNote->SetDate( aDate );
+        }
         pNote->SetAuthor( mxAnnotationData->maAuthor );
     }