change_flag: fix clearing text

We need to restore the focus before clearing the text,
otherwise the Message Window ignores our request.

When the focus is on the Message Window, someone else must be in
control, e.g. for data entry or asking the user a question.

flags.c

@@ -454,8 +454,8 @@ int mutt_change_flag(struct Mailbox *m, struct EmailList *el, bool bf)
     event = mutt_getch();
   } while (event.ch == -2); // Timeout
 
-  msgwin_clear_text();
   window_set_focus(old_focus);
+  msgwin_clear_text();
 
   if (event.ch < 0) // SIGINT, Abort key (Ctrl-G)
     return -1;