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_stun.h

@@ -24,6 +24,7 @@ public:
 	NetworkAddress local_addr;         ///< Local addresses of the socket.
 
 	NetworkRecvStatus CloseConnection(bool error = true) override;
+	~ClientNetworkStunSocketHandler() override;
 	void SendReceive();
 
 	void Connect(const std::string &token, uint8 family);