Bug 136553 [regression]Preview error when set invalid group interval.
Description: Preview error when set invalid group interval. Steps to reproduce: 1. Insert a table 2. Add a group on number column, set interval to Year,1 3. Preview 4. Edit group on string column set interval to Prefix,1 5. Preview Expected result: Error msg about invalid group interval. Actual result: Error happened while running the report
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/DataGenerationEngine.java
import org.eclipse.birt.report.engine.executor.ExecutionContext;
import org.eclipse.birt.report.engine.ir.Report;
import org.mozilla.javascript.Scriptable;
public class DataGenerationEngine extends AbstractDataEngine
{
	/*
	 * need not be stored in report document.
	 */
	protected HashMap queryMap = new HashMap( );
	/**
	 * output stream used to save the resultset relations
	 */
	private DataOutputStream dos;
	public DataGenerationEngine( ExecutionContext ctx, IDocArchiveWriter writer )
	{
		context = ctx;
		try
		{
			Scriptable scope = context.getScope( );
			
			
			context.registerBean( "row", new NativeRowObject( scope, rsets ) );
			
			DataEngineContext dteContext = DataEngineContext.newInstance(
					DataEngineContext.MODE_GENERATION, ctx.getSharedScope( ),
					null, writer );
			dteEngine = DataEngine.newDataEngine( dteContext );
		}
		catch ( Exception ex )
		{