openssl: Ensure the thread ID is never zero

This might otherwise cause problems because OpenSSL tries to lock
mutexes recursively if it assumes the lock is held by a different
thread e.g. during FIPS initialization.

src/libstrongswan/plugins/openssl/openssl_plugin.c

@@ -129,7 +129,9 @@ static void destroy_function(struct CRYPTO_dynlock_value *lock,
  */
 static unsigned long id_function(void)
 {
-	return (unsigned long)thread_current_id();
+	/* ensure the thread ID is never zero, otherwise OpenSSL might try to
+	 * acquire locks recursively */
+	return 1 + (unsigned long)thread_current_id();
 }
 
 /**