utils: localtime is not threadsafe, use localtime_r

utils.cpp

@@ -161,13 +161,13 @@ std::string utils::regex_callback_replacer(std::regex regex, const std::string &
 
 std::string utils::toISODate(time_t t)
 {
-	struct tm *lt = localtime(&t);
+	struct tm lt;
-	if(lt == nullptr)
+	if(localtime_r(&t, &lt) == nullptr)
 	{
 		return {};
 	}
 	char result[20];
-	size_t x = strftime(result, sizeof(result), "%Y-%m-%d %H:%M:%S", lt);
+	size_t x = strftime(result, sizeof(result), "%Y-%m-%d %H:%M:%S", &lt);
 	if(x == 0)
 	{
 		return {};