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/api/impl/DataExtractionTask.java
{
			try
			{
				IQueryResults queryResults = dataEngine.getQueryResults( queryResultName );
				
				assert queryResults.getResultIterator() != null;
				
				ExtractionResults results = new ExtractionResults( queryResults.getResultIterator() 
						, selectedColumns, query.getRowExpressions() );
				resultMetaList.add( results.getResultMetaData() );
				return results;
				
			}
			catch ( BirtException e )
			{
				e.printStackTrace();
			}
		}
		else
		{
			DataSetID parentId = dataSetId.getParentID( );
			assert parentId != null;
			try
			{
				queryResultName = parentId.getDataSetName( );
				DataSetID parId = parentId;
				while( queryResultName == null && parId != null )
				{
					parId = parId.getParentID();
					if( parId != null )