io: store current directory iterator filepath as a b_path

io/sys/windows/directory.c

@@ -153,8 +153,23 @@ static void cleanup_iterator(struct b_directory_iterator *it)
 
 static void update_iterator_data(struct b_directory_iterator *it)
 {
+	if (it->filepath) {
+		b_path_release(B_PATH(it->filepath));
+		it->filepath = NULL;
+	}
+
 	struct iteration_state *state = get_iteration_state(it->_z);
 	it->filename = state->data.cFileName;
+
+	struct b_path *filename = b_path_create_from_cstr(it->filename);
+
+	const struct b_path *parts[] = {
+		state->search_path,
+		filename,
+	};
+
+	it->filepath
+		= b_path_join(parts, sizeof parts / sizeof parts[0]);
 }
 
 static bool move_into_directory(struct b_directory_iterator *it, const char *dir_name)