When doing a silent old config, don't check if stdin was redirected. ct-ng doesn't use this feature, and even better yet, it makes explicit use of redirecting both stdin and stdout at aome moments.

kconfig/conf.c

@@ -503,7 +503,6 @@ int main(int ac, char **av)
 			break;
 		case 's':
 			input_mode = ask_silent;
-			valid_stdin = isatty(0) && isatty(1) && isatty(2);
 			break;
 		case 'd':
 			input_mode = set_default;