Bug 176582 "Show Lines as Curves" does not work correctly for Area Chart [0001]
Description: "Show Lines as Curves" does not work correctly for Area Chart. Build number: 2.2.0.v20070307-1128 Steps to reproduce: 1. New a Area Chart. 2. In "Format Chart" tab, select Series->Value (Y) Series, tick and untick "Show Lines as Curves" checkbox. Expected result: Null value point e is treated the same when tick and untick "Show Lines as Curves" checkbox. Actual result: Null value point e is treated differently (see the screenshot). Error log: N/A
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/render/CurveRenderer.java
* 
	 * @param ipr
	 * @param x1
	 * @param y1
	 * @param x2
	 * @param y2
	 * @throws RenderingException
	 */
	private final void plotPlane( IPrimitiveRenderer ipr, double x1, double y1,
			double x2, double y2, double z1, double z2, boolean drawSide,
			boolean leftSide ) throws ChartException
	{
		if ( bRendering3D )
		{
			final Polygon3DRenderEvent pre = (Polygon3DRenderEvent) ( (EventObjectCache) ipr ).getEventObject( oSource,
					Polygon3DRenderEvent.class );
			pre.setOutline( null );
			pre.setDoubleSided( true );
			pre.setBackground( tapeColor );
			if ( !leftSide )
			{
				loa3d[0].set( x1 + kError, y1 + kError, z1 );
				loa3d[1].set( x2 + kError, y2 + kError, z2 );
				loa3d[2].set( x2 + kError, y2 + kError, z2 - dTapeWidth );
				loa3d[3].set( x1 + kError, y1 + kError, z1 - dTapeWidth );
				pre.setPoints3D( loa3d );
				dc.addPlane( pre, PrimitiveRenderEvent.FILL );
			}
			if ( drawSide )
			{