archive_match: Use correct data type for iterator

archive_match: Use correct data type for iterator

Iterating over a size_t with unsigned could lead to an endless loop
while adding uid/gid to a list which already counts 4 billion
entries.

I doubt that this can ever happen, given that the routines become
very slow with insertions, but better be safe than sorry.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>