Avoid an exception due to some bad logic in the DNS resolution mechanic

fix #3207

louloulibs/network/dns_socket_handler.cpp

@@ -42,6 +42,7 @@ bool DNSSocketHandler::is_connected() const
 
 void DNSSocketHandler::remove_from_poller()
 {
+  if (this->poller->is_managing_socket(this->socket))
     this->poller->remove_socket_handler(this->socket);
 }
 

louloulibs/network/poller.cpp

@@ -226,3 +226,8 @@ size_t Poller::size() const
 {
   return this->socket_handlers.size();
 }
+
+bool Poller::is_managing_socket(const socket_t socket) const
+{
+  return (this->socket_handlers.find(socket) != this->socket_handlers.end());
+}

louloulibs/network/poller.hpp

@@ -74,6 +74,10 @@ public:
    * Returns the number of SocketHandlers managed by the poller.
    */
   size_t size() const;
+  /**
+   * Whether the given socket is managed by the poller
+   */
+   bool is_managing_socket(const socket_t socket) const;
 
 private:
   /**