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
* @return
	 */
	private boolean isGroupFilter( IFilterDefinition filter)
	{
		IBaseExpression expr = filter.getExpression( );
		if ( expr instanceof IConditionalExpression )
		{
			String expr4Exception = ( (ConditionalExpression) expr ).getExpression( )
					.getText( );
			try
			{
				new FilterExpressionParser( null, null ).compileFilterExpression( expr4Exception );
			}
			catch ( DataException e )
			{
				return true;
			}
		}
		return false;
	}
	
	/*
	 * @see org.eclipse.birt.data.engine.impl.IQueryExecutor#getResultMetaData()
	 */
	public IResultMetaData getResultMetaData( ) throws DataException
	{
		assert odiQuery instanceof IPreparedDSQuery
				|| odiQuery instanceof ICandidateQuery
				|| odiQuery instanceof JointDataSetQuery;