Bug 153523 OK button in parameter dialog is enabled without default value in combo-box
Description: OK button in parameter dialog is enabled without default value in combo-box Steps to reproduce: 1. New a report parameter, combo-box. 2. Click New button, input abc as value, click OK 3. Set abc as default value and close Edit Parameter dialog. 4. New a data source and dataset 5. Edit the parameter, remove abc value and import values from dataset Expected result: OK button is disabled for there is no default value. Actual result: OK button is enabled.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
SelectionChoiceDialog dialog = new SelectionChoiceDialog( Messages.getString("ParameterDialog.SelectionDialog.New") ); 
			dialog.setInput( choice );
			dialog.setValidator( new SelectionChoiceDialog.ISelectionChoiceValidator( ) {
				public String validate( String displayLabel, String value )
				{
					return validateChoice( null, displayLabel, value );
				}
			} );
			if ( dialog.open( ) == Dialog.OK )
			{
				choice.setValue( convertToStandardFormat( choice.getValue( ) ) );
				choiceList.add( choice );
				return true;
			}
			return false;
		}
		public boolean removeItem( Object[] elements )
		{
			for ( int i = 0; i < elements.length; i++ )
			{
				choiceList.remove( elements[i] );
			}
			return true;
		}
	};
	private Text listLimit;
	/**
	 * Create a new parameter dialog with given title under the active shell
	 * 
	 * @param title