fix(terminal): schedule frame before flushing buffered output

Signed-off-by: fufesou <linlong1266@gmail.com>

flutter/lib/models/terminal_model.dart

@@ -458,6 +458,7 @@ class TerminalModel with ChangeNotifier {
         _markViewReady();
       }
     });
+    WidgetsBinding.instance.ensureVisualUpdate();
   }
 
   void _markViewReady() {