Re: [PATCH v5 0/5] for-each-ref: introduce seeking functionality via '--start-after'

[Kyle Lippincott <spectral@google.com>]

There's something in this series that's triggering an msan warning in
t/t6302-for-each-ref-filter:

==2147==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x562a64e923cc in cache_ref_iterator_advance refs/ref-cache.c:409:27
    #1 0x562a64e88dc0 in ref_iterator_advance refs/iterator.c:15:9
    #2 0x562a64e88dc0 in merge_ref_iterator_advance refs/iterator.c:164:13
    #3 0x562a64e8850b in ref_iterator_advance refs/iterator.c:15:9
    #4 0x562a64e85f5a in files_ref_iterator_advance refs/files-backend.c:902:15
    #5 0x562a64e88bb4 in ref_iterator_advance refs/iterator.c:15:9
    #6 0x562a64e88bb4 in do_for_each_ref_iterator refs/iterator.c:478:15
    #7 0x562a64e64593 in for_each_fullref_with_seek ref-filter.c:2718:9
    #8 0x562a64e5cfe8 in for_each_fullref_in_pattern ref-filter.c
    #9 0x562a64e5cfe8 in do_filter_refs ref-filter.c:3263:9
    #10 0x562a64e5d7fc in filter_and_format_refs ref-filter.c:3364:3
    #11 0x562a64af0235 in cmd_for_each_ref builtin/for-each-ref.c:115:2
    #12 0x562a64a3ebdc in run_builtin git.c:480:11
    #13 0x562a64a3d342 in handle_builtin git.c:746:9
    #14 0x562a64a3be33 in run_argv git.c:813:4
    #15 0x562a64a3be33 in cmd_main git.c:953:19
    #16 0x562a64c2f12f in main common-main.c:9:11

SUMMARY: MemorySanitizer: use-of-uninitialized-value
refs/ref-cache.c:409:27 in cache_ref_iterator_advance

Unfortunately I can't provide great instructions for reproducing this
locally, because it relies on our internal build stack (which uses
blaze). Getting MemorySanitizer running can be quite annoying, though
you might not have any issues if this test doesn't invoke any third
party libraries (like zlib).

I need to sign off for the night soon, but if this isn't sufficient
enough information to identify what's happening here, I can try to dig
deeper tomorrow. This run was executed on an import of upstream commit
4ea3c74afd42a503b3e0d60e1fec33bc0431e7bc (Junio's merge of this
series)