Bug 203709 NullPointerException in TableAreaLayout
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/layout/pdf/cache/TableAreaLayout.java
/*
		 * 1. scan current row and calculate row height
		 * 2. update the height of drop cells
		 * 3. update the height of row
		 */
		
		if(rows.size( )==0 || !hasDropCell)
		{
			return 0;
		}
		Row row = (Row)rows.getCurrent( );
		int rowHeight = row.getArea( ).getHeight( );
		int height = rowHeight;
		boolean hasDropCell = false;
		
		for(int i=startCol; i<=endCol; i++)
		{
			CellArea cell = row.getCell( i );
			if(cell!=null)
			{
				if(isDropCell( cell ) || cell.getRowSpan( )>1 )
				{
					if ( cell instanceof DummyCell )
					{
						height = Math.max( height, cell.getHeight() + rowHeight );
					}
					else
					{
						height = Math.max( height, cell.getHeight( ) );