[lmi] Transient git error

[Greg Chicares]

In a freshly-built chroot, 'git fetch --all' initially failed as
follows...

Could not access submodule '3rdparty/wxWidgets' at commit 938b8a6ae
Could not access submodule '3rdparty/wxpdfdoc' at commit 8752a7da6
Could not access submodule '3rdparty/xmlwrapp' at commit 8752a7da6
fatal: remote error: upload-pack: not our ref 
f279b417f431db35c90a9813d3f2e6abfaeead30
fatal: remote error: upload-pack: not our ref 
9325bced99d79d78658a6c7a620a34f73f4abfa5
Errors during submodule fetch:
        third_party/libxslt
        third_party/libxml2
error: could not fetch xanadu

...but then repeating the same command verbatim succeeded.

Furthermore, the build succeeds after these subsequent commands:
  $ git cherry-pick xanadu/wx-upgrade..xanadu/all-libs-upgrade
  $ git submodule update --recursive                  
  Submodule path 'third_party/libxml2': checked out 
'f507d167f1755b7eaea09fb1a44d29aab828b6d1'
  Submodule path 'third_party/libxslt': checked out 
'5eca7fb65b7337409a02f9f94fde608edf7d1b0a'
  Submodule path 'third_party/xmlwrapp': checked out 
'cdb0e46338c00a04f40a0d0ef1a64ce6925e45da'
(where the cherry-pick command specifies two commits in order
to skip the interim 'wx-upgrade' commit that had already been
pushed to master). The submodule SHA1s above match those in
the corresponding commits, and running './install_msw.sh' to
rebuild everything (including those libraries) succeeds.

AFAICT, the problem fixed itself somehow, but naturally I wonder
how this could be.

The remainder of this message consists only of the full session,
with only the successful fetch of 'shangri-la' snipped:

/opt/lmi/src/lmi[0]$git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
/opt/lmi/src/lmi[0]$git fetch --all
Fetching origin
Fetching xanadu
remote: Enumerating objects: 14583, done.
remote: Counting objects: 100% (4671/4671), done.
remote: Compressing objects: 100% (94/94), done.
remote: Total 14583 (delta 4590), reused 4645 (delta 4575), pack-reused 9912
Receiving objects: 100% (14583/14583), 6.30 MiB | 10.72 MiB/s, done.
Resolving deltas: 100% (6857/6857), completed with 871 local objects.
>From https://github.com/vadz/lmi
 * [new branch]          all-libs-upgrade           -> xanadu/all-libs-upgrade
 * [new branch]          any_member-opt             -> xanadu/any_member-opt
 * [new branch]          automake-tests             -> xanadu/automake-tests
 * [new branch]          better-so-fix              -> xanadu/better-so-fix
 * [new branch]          census-view-columns-opt    -> 
xanadu/census-view-columns-opt
 * [new branch]          census-view-only-grid      -> 
xanadu/census-view-only-grid
 * [new branch]          census-view-optimize       -> 
xanadu/census-view-optimize
 * [new branch]          ci-ccache                  -> xanadu/ci-ccache
 * [new branch]          ci-libunwind               -> xanadu/ci-libunwind
 * [new branch]          clang-tag-mismatch         -> xanadu/clang-tag-mismatch
 * [new branch]          currency-class             -> xanadu/currency-class
 * [new branch]          direct-pdf-gen-master      -> 
xanadu/direct-pdf-gen-master
 * [new branch]          disable-xmlwrapp-bootstrap -> 
xanadu/disable-xmlwrapp-bootstrap
 * [new branch]          fix-ci-apt-install         -> xanadu/fix-ci-apt-install
 * [new branch]          fix-shadow                 -> xanadu/fix-shadow
 * [new branch]          fpenv-non-x87              -> xanadu/fpenv-non-x87
 * [new branch]          git-svn                    -> xanadu/git-svn
 * [new branch]          group-quotes-fields        -> 
xanadu/group-quotes-fields
 * [new branch]          gui-test                   -> xanadu/gui-test
 * [new branch]          input-seq-ui               -> xanadu/input-seq-ui
 * [new branch]          install-wx-v2              -> xanadu/install-wx-v2
 * [new branch]          latest-libxml2             -> xanadu/latest-libxml2
 * [new branch]          master                     -> xanadu/master
 * [new branch]          master-new                 -> xanadu/master-new
 * [new branch]          more-pdf-pagination        -> 
xanadu/more-pdf-pagination
 * [new branch]          new-boost                  -> xanadu/new-boost
 * [new branch]          no-cast-qual-for-wx        -> 
xanadu/no-cast-qual-for-wx
 * [new branch]          nullptr                    -> xanadu/nullptr
 * [new branch]          parallel-coding-rules-test -> 
xanadu/parallel-coding-rules-test
 * [new branch]          pch-fixes                  -> xanadu/pch-fixes
 * [new branch]          pcre                       -> xanadu/pcre
 * [new branch]          pdf-table-layout           -> xanadu/pdf-table-layout
 * [new branch]          pdf_gen_errors             -> xanadu/pdf_gen_errors
 * [new branch]          shellchecl-gha-ci          -> xanadu/shellchecl-gha-ci
 * [new branch]          single-file-menu           -> xanadu/single-file-menu
 * [new branch]          skin-select                -> xanadu/skin-select
 * [new branch]          split-fund-report          -> xanadu/split-fund-report
 * [new branch]          std-filesystem             -> xanadu/std-filesystem
 * [new branch]          stream-cast-libcxx-bug     -> 
xanadu/stream-cast-libcxx-bug
 * [new branch]          travis-ci                  -> xanadu/travis-ci
 * [new branch]          tt                         -> xanadu/tt
 * [new branch]          uniform-init               -> xanadu/uniform-init
 * [new branch]          use-ctre                   -> xanadu/use-ctre
 * [new branch]          use-std-regex              -> xanadu/use-std-regex
 * [new branch]          value-str-template-divisor -> 
xanadu/value-str-template-divisor
 * [new branch]          valyuta/002                -> xanadu/valyuta/002
 * [new branch]          wx-only-submodules         -> xanadu/wx-only-submodules
 * [new branch]          wx-submodules              -> xanadu/wx-submodules
 * [new branch]          wx-update                  -> xanadu/wx-update
 * [new branch]          wx-upgrade                 -> xanadu/wx-upgrade
 * [new branch]          wx_test-hygiene            -> xanadu/wx_test-hygiene
 * [new branch]          xmlwrapp-submodule         -> xanadu/xmlwrapp-submodule
 * [new tag]             new-cygwin-makefiles       -> new-cygwin-makefiles
Fetching submodule third_party/libxml2
Fetching submodule third_party/libxslt
Could not access submodule '3rdparty/wxWidgets' at commit 938b8a6ae
Could not access submodule '3rdparty/wxpdfdoc' at commit 8752a7da6
Could not access submodule '3rdparty/xmlwrapp' at commit 8752a7da6
fatal: remote error: upload-pack: not our ref 
f279b417f431db35c90a9813d3f2e6abfaeead30
fatal: remote error: upload-pack: not our ref 
9325bced99d79d78658a6c7a620a34f73f4abfa5
Errors during submodule fetch:
        third_party/libxslt
        third_party/libxml2
error: could not fetch xanadu
Fetching shangri-la
[...no error observed with 'shangri-la'...]
/opt/lmi/src/lmi[1]$git fetch --all
Fetching origin
Fetching xanadu
Fetching shangri-la