Bug 121687 Exception throws when export data in table which inside a grid cell.
Description: Exception throws when export data in table which inside a grid cell. Steps to reproduce: 1. insert a grid. 2. insert one table to one grid cell. 3. insert another table to the other grid cell. 4. export data in two tables. Expected result: Data are exported. Actual result: Exception in: ReportEngineService.getMetaData( )
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/parser/EngineIRVisitor.java
GraphicMasterPageDesign page = new GraphicMasterPageDesign( );
		setupMasterPage( page, handle );
		
		page.setColumns( handle.getColumnCount( ) );
		DimensionType spacing = createDimension( handle.getColumnSpacing( ) );
		page.setColumnSpacing( spacing );
		
		SlotHandle contentSlot = handle.getContent( );
		for ( int i = 0; i < contentSlot.getCount( ); i++ )
		{
			apply( contentSlot.get( i ) );
			if ( currentElement != null )
			{
				page.addContent( (ReportItemDesign) currentElement );
			}
		}
		currentElement = page;
	}
	public void visitSimpleMasterPage( SimpleMasterPageHandle handle )
	{
		SimpleMasterPageDesign page = new SimpleMasterPageDesign( );
		
		setupMasterPage( page, handle );
		page.setHeaderHeight( createDimension( handle.getHeaderHeight( ) ) );
		page.setFooterHeight( createDimension( handle.getFooterHeight( ) ) );
		page.setShowFooterOnLast(handle.showFooterOnLast());
		page.setShowHeaderOnFirst(handle.showFooterOnLast());
		SlotHandle headerSlot = handle.getPageHeader( );
		for ( int i = 0; i < headerSlot.getCount( ); i++ )
		{