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
SlotHandle columnSlot = handle.getColumns( );
		for ( int i = 0; i < columnSlot.getCount( ); i++ )
		{
			ColumnHandle columnHandle = (ColumnHandle) columnSlot.get( i );
			apply( columnHandle );
			if ( currentElement != null )
			{
				ColumnDesign columnDesign = (ColumnDesign) currentElement;
				for ( int j = 0; j < columnHandle.getRepeatCount( ); j++ )
				{
					grid.addColumn( columnDesign );
				}
			}
		}
		
		SlotHandle rowSlot = handle.getRows( );
		for ( int i = 0; i < rowSlot.getCount( ); i++ )
		{
			apply( rowSlot.get( i ) );
			if ( currentElement != null )
			{
				grid.addRow( (RowDesign) currentElement );
			}
		}
		new TableItemDesignLayout( ).layout( grid );
		currentElement = grid;
	}
	public void visitImage( ImageHandle handle )
	{