Bug 145478 Unable "Select Value" in the Join data set's filter
Step to reproduce: 1.new a join data set(please use the attached file) 2.right click the dataset and click the Edit 3.go to the Filter pane and set a filer 4.click the list of Value1 Actual result: A warning pop up and cant select Value.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/data/ui/util/DataSetProvider.java
* 
	 * @param ds
	 * @param columns
	 */
	public DataSetViewData[] getCachedDataSetItemModel( DataSetHandle ds )
	{
		DataSetViewData[] result = (DataSetViewData[]) this.htColumns.get( ds );
		if ( result == null )
			result = new DataSetViewData[0];
		return result;
	}
	
	/**
	 * 
	 * @param ds
	 * @param column
	 */
	private void updateModelColumn( DataSetHandle ds, DataSetViewData column )
	{
		PropertyHandle resultSetColumns = ds.getPropertyHandle( DataSetHandle.RESULT_SET_PROP );
		
		Iterator iterator = resultSetColumns.iterator( );
		boolean found = false;
		while ( iterator.hasNext( ) )
		{
			ResultSetColumnHandle rsColumnHandle = (ResultSetColumnHandle) iterator.next( );
			assert rsColumnHandle.getPosition( ) != null;
			if ( rsColumnHandle.getPosition( ).intValue( ) == column.getPosition( ) )
			{
				if ( rsColumnHandle.getColumnName( ) != null