Bug 124251 the data cann't been exported.
Description: the data cann't been exported. Steps to reproduce: 1. new a report 2. new a datasource and a data set(DS_A) 3. use an external library 4. drag a table to the report layout from the imported library 5. insert an another table into the layout of the report and bind the data set(DS_A) 6. preview in the 'Web Viewer' and export the data Actual result: The data can been exported. Expect result: The data can been exporteded
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/DataExtractionTask.java
assert rptItem != null;
		
		validateSelectedColumns( rptItem.getQuery( ) );
		
		
		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();