Added semi-workaround method for network thread shutdown:

Currently closing game while network thread is waiting for something is
very bug-prone, since network thread may resume during shutdown and
access partially destroyed client state.

Now if exit has been requested, the very first step would be semi-
graceful shutdown of network thread (via exception throwing). This may
in theory skip some cleanup in non-RAII code, but since game is shutting
down this does not matters much.

This logic applies to:
- shutting down while network thread is waiting for dialogs
- shuttind down while network thread waiting for animations in combat

client/Client.cpp

@@ -346,6 +346,19 @@ void CClient::save(const std::string & fname)
 	sendRequest(&save_game, PlayerColor::NEUTRAL);
 }
 
+void CClient::endNetwork()
+{
+	if (CPlayerInterface::battleInt)
+		CPlayerInterface::battleInt->endNetwork();
+
+	for(auto & i : playerint)
+	{
+		auto interface = std::dynamic_pointer_cast<CPlayerInterface>(i.second);
+		if (interface)
+			interface->endNetwork();
+	}
+}
+
 void CClient::endGame()
 {
 #if SCRIPTING_ENABLED