Add a strtoul() wrapper

src/zyklonb.c

@@ -1418,10 +1418,8 @@ irc_try_reconnect (struct bot_context *ctx)
 	const char *delay_str = str_map_find (&ctx->config, "reconnect_delay");
 	hard_assert (delay_str != NULL);  // We have a default value for this
 
-	char *end_ptr;
-	errno = 0;
-	long delay = strtol (delay_str, &end_ptr, 10);
-	if (errno != 0 || end_ptr == delay_str || *end_ptr)
+	unsigned long delay;
+	if (!xstrtoul (&delay, delay_str, 10))
 	{
 		print_error ("invalid configuration value for `%s'",
 			"reconnect_delay");