fix validation error in lineChart export, related tdf#57832

Change-Id: I282a6f476830d688837a9731234aaba37a13de16
Reviewed-on: https://gerrit.libreoffice.org/46673Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
(cherry picked from commit 70f9eb96)
Reviewed-on: https://gerrit.libreoffice.org/46767Reviewed-by: Eike Rathke <erack@redhat.com>

oox/source/export/chartexport.cxx

@@ -1691,9 +1691,9 @@ void ChartExport::exportLineChart( const Reference< chart2::XChartType >& xChart
         pFS->startElement( FSNS( XML_c, nTypeId ),
                 FSEND );
 
-        exportVaryColors(xChartType);
-
         exportGrouping( );
+
+        exportVaryColors(xChartType);
         // TODO: show marker symbol in series?
         bool bPrimaryAxes = true;
         exportSeries(xChartType, *itr, bPrimaryAxes);