Bug 210635 Incorrect preview of chart after reverse categories.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/computation/withaxes/PlotWith2DAxes.java
DataSetIterator[] dsi = new DataSetIterator[ssl.getSeriesCount( ax )];
			if ( alSeriesGroupsPerAxis == null )
			{
				throw new ChartException( ChartEnginePlugin.ID,
						ChartException.DATA_SET,
						"exception.internal.stack.series.setup", 
						new Object[]{
							ax
						},
						Messages.getResourceBundle( rtc.getULocale( ) ) );
			}
			logger.log( ILogger.INFORMATION,
					Messages.getString( "info.processing.stacked.info", 
							new Object[]{
								ax
							},
							rtc.getULocale( ) ) );
			int iSeriesIndex, iDataSetCount = ssl.getUnitCount( );
			for ( int k = 0; k < iDataSetCount; k++ ) 
			{
				iSeriesIndex = 0;
				for ( int i = 0; i < alSeriesGroupsPerAxis.size( ); i++ )
				{
					sg = (StackGroup) alSeriesGroupsPerAxis.get( i );
					alSeriesPerGroup = sg.getSeries( );
					iSeriesPerGroup = alSeriesPerGroup.size( );
					if ( iSeriesPerGroup > 0 )
					{
						se = (Series) alSeriesPerGroup.get( 0 );
						ds = se.getDataSet( );