Fix possible crash on closing game from main menu

client/Client.cpp

@@ -348,7 +348,9 @@ void CClient::save(const std::string & fname)
 
 void CClient::endNetwork()
 {
-	CGI->mh->endNetwork();
+	if (CGI->mh)
+		CGI->mh->endNetwork();
+
 	if (CPlayerInterface::battleInt)
 		CPlayerInterface::battleInt->endNetwork();