OOB controls fix 1 (#2492)

Author: FeodorFitsner

package/lib/flet.dart

@@ -4,6 +4,7 @@ export 'src/control_factory.dart';
 export 'src/controls/create_control.dart';
 export 'src/controls/flet_control_stateful_mixin.dart';
 export 'src/controls/flet_control_stateless_mixin.dart';
+export 'src/controls/flet_store_mixin.dart';
 export 'src/flet_app.dart';
 export 'src/flet_app_errors_handler.dart';
 export 'src/flet_server.dart';

package/lib/src/controls/create_control.dart

@@ -722,7 +722,7 @@ Widget createWidget(Key? key, ControlViewModel controlView, Control? parent,
           control: controlView.control,
           parentDisabled: parentDisabled);
     default:
-      throw Exception("Unknown control type: ${controlView.control.type}");
+      return ErrorControl("Unknown control: ${controlView.control.type}");
   }
 }