fixes for msvc

tools/dhtnode.cpp

@@ -516,7 +516,10 @@ int
 main(int argc, char **argv)
 {
 #ifdef _MSC_VER
-    gnutls_global_init();
+    if (auto err = gnutls_global_init()) {
+        std::cerr << "Failed to initialize GnuTLS: " << gnutls_strerror(err) << std::endl;
+        return EXIT_FAILURE;
+    }
 #endif
     auto params = parseArgs(argc, argv);
     if (params.help) {