Bug 188029 Top face is missing in Area chart of 2D+ with negative values
Top face is missing in Area chart of 2D+ with negative values. Please see attached screenshot.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/computation/withaxes/StackedSeriesLookup.java
* The constructor.
	 */
	StackedSeriesLookup( RunTimeContext rtc )
	{
		htAxisToStackGroups = new Hashtable( );
		htSeriesToStackGroup = new Hashtable( );
	}
	/**
	 * 
	 * @param ax
	 * @return
	 */
	public final ArrayList getStackGroups( Axis ax )
	{
		return (ArrayList) htAxisToStackGroups.get( ax );
	}
	/**
	 * 
	 * @param ax
	 * @return
	 */
	public final int getSeriesCount( Axis ax )
	{
		final ArrayList alSG = (ArrayList) htAxisToStackGroups.get( ax );
		if ( alSG == null || alSG.isEmpty( ) )
		{
			return 0;
		}
		int iCount = 0;
		StackGroup sg;