[ox/std] Fix ox::join to work with list types that done have a front function

(synced from b6ed919b01)

src/ox/std/fmt.hpp

@@ -207,7 +207,7 @@ constexpr Result<T> join(auto d, const auto &list) {
 		return T("");
 	}
 	T out;
-	out += list.front().value;
+	out += list[0];
 	for (auto i = 1ul; i < list.size(); ++i) {
 		out += d;
 		out += list[i];