Fix: use-after-free after ClientNetworkCoordinatorSocketHandler::CloseAllConnections() (#9534)

The function clears all stun-handlers. This causes all of those
objects to be destroyed.
A handler can have a pending connecter, which was only killed in
case CloseConnection() was called. This is never the case when
the object is destroyed. In result, the connecter could finish
and cause a use-after-free by calling into the (now deleted)
handler.

src/network/network_turn.h

@@ -30,6 +30,7 @@ public:
 	ClientNetworkTurnSocketHandler(const std::string &token, uint8 tracking_number, const std::string &connection_string) : token(token), tracking_number(tracking_number), connection_string(connection_string) {}
 
 	NetworkRecvStatus CloseConnection(bool error = true) override;
+	~ClientNetworkTurnSocketHandler() override;
 	void SendReceive();
 
 	void Connect();