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
for ( int i = 0; i < alSG.size( ); i++ )
		{
			sg = (StackGroup) alSG.get( i );
			iCount += sg.alSeries.size( );
		}
		return iCount;
	}
	/**
	 * @param se
	 * @return The stack group associated with a specified Series
	 */
	public final StackGroup getStackGroup( Series se )
	{
		return (StackGroup) htSeriesToStackGroup.get( se );
	}
	/**
	 * @param sg
	 * @param iUnitIndex
	 * @return An AxisUnit corresponding to a given stack group and specified
	 *         unit index
	 */
	public final AxisSubUnit getSubUnit( StackGroup sg, int iUnitIndex )
	{
		if ( sg == null || !htSeriesToStackGroup.contains( sg ) )
		{
			return null;
		}
		
		if ( sg.alUnitPositions == null )
		{