optimize the datepicker about erase

src/main/webapp/resource/datepickerRefactor/js/jquery.ui.datepickerRefactor.js

@@ -891,6 +891,9 @@ $.extend(Datepicker.prototype, {
 			(period == 'M' ? this._get(inst, 'showCurrentAtPos') : 0), // undo positioning
 			period);
 		this._updateDatepicker(inst);
+		if(!targetDateInput.val()){
+			$.datepicker._eraseAllData();
+		}
 	},
 
 	/* Action for current link. */