adds a check whether the socket is open before sending a message

src/xrpld/overlay/detail/PeerImp.cpp

@@ -240,9 +240,13 @@ PeerImp::send(std::shared_ptr<Message> const& m)
 {
     if (!strand_.running_in_this_thread())
         return post(strand_, std::bind(&PeerImp::send, shared_from_this(), m));
+
     if (gracefulClose_)
         return;
 
+    if (!socket_.is_open())
+        return;
+
     auto validator = m->getValidatorKey();
     if (validator && !squelch_.expireSquelch(*validator))
     {