rerere: don't segfault on failure to open rr-cache The rr-cache directory should always exist if we are doing garbage collection (earlier code paths check this explicitly), but we may not necessarily succeed in opening it (for example, due to permissions problems). In that case, we should print an error message rather than simply segfaulting. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>