Bug 139346 Using isTopN in table inside list group header doesn't work.
Description: Using isTopN in table inside list group header doesn't work. Steps to reproduce: 1.Insert a list with a group 2.Insert a table to list group header 3.Using Total.isTopN(row[],2,null,0) as filter expression in table item. 4.Preview Result: Only the first group displayed top 2 records, other groups kept display all records.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/QueryExecutor.java
if ( odiQuery instanceof IPreparedDSQuery )
		{
			if ( ( (IPreparedDSQuery) odiQuery ).getResultClass( ) != null )
				return new ResultMetaData( ( (IPreparedDSQuery) odiQuery ).getResultClass( ) );
			else
			    return null;
		}
		else if ( odiQuery instanceof JointDataSetQuery )
		{
			return new ResultMetaData( ( (JointDataSetQuery) odiQuery ).getResultClass( ) );
		}
		else
		{
			return new ResultMetaData( ( (ICandidateQuery) odiQuery ).getResultClass( ) );
		}
	}
	
	/*
	 * @see org.eclipse.birt.data.engine.impl.IQueryExecutor#execute()
	 */
	public void execute( IEventHandler eventHandler ) throws DataException
	{
		logger.logp( Level.FINER,
				QueryExecutor.class.getName( ),
				"execute",
				"Start to execute" );
		if(this.isExecuted)
			return;
		ExecutorHelper helper = new ExecutorHelper( this.queryScope );
		helper.setParent( this.parentHelper );