Bug 121682 Exception throws when export data from table containing highlight/map.
Description: Exception throws when export data from attached report. Steps to reproduce: 1. I add a table which has a group, a highlight rule and a map rule in group row. 2. Preview the report attached. 3. Export the data in table. Expected result: Data are exported. Actual result: Exception in: ReportEngineService.getMetaData( )
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/DataExtractionTask.java
while ( iter.next( ) && i++ < rowid ) 		;
				
				IResultIterator subIter = iter.getSecondaryIterator( dataSetId
						.getQueryName( ), executionContext.getScope( ) );
				
				ExtractionResults results = new ExtractionResults( subIter, 
						selectedColumns, query.getRowExpressions() );
				
				resultMetaList.add( results.getResultMetaData());
				return results;
			}
			catch( BirtException be )
			{
				be.printStackTrace( );
			}
		}
		
		return null;
	}
	
	private void validateSelectedColumns( IBaseQueryDefinition query )
			throws EngineException
	{
		assert query != null;
		Collection exprs = query.getRowExpressions( );
		if ( selectedColumns != null )
		{
			for ( int i = 0; i < selectedColumns.length; i++ )
			{
				boolean findColumn = false;