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
DataID dataId = instanceId.getDataID();
		InstanceID instId = instanceId;
		while( instId != null && dataId == null ){
			instId = instId.getParentID( );
			if( instId != null )
			{
				dataId = instId.getDataID();
			}
		}
		
		if(dataId == null)
			return null;
		
		DataSetID dataSetId = dataId.getDataSetID( );
		assert dataSetId != null;
		
		String queryResultName = dataSetId.getDataSetName( );
		
		if( resultMetaList == null )
		{
			resultMetaList = new ArrayList( );
		}
		else
		{
			resultMetaList.clear();
		}
		
		if ( queryResultName != null )