[PATCH v2 0/3] fetch: fix segfault, missing docs in --negotiate-only

Fix a segfault in recent code, per v1's: https://lore.kernel.org/git/cover-0.3-00000000000-20210630T163329Z-avarab@gmail.com/

Fixes a stray "cat err" that snuck out of the lab and into the test, spotted by Jonathan Tan.

Junio: You picked this up as ab/fetch-negotiate-segv-fix and it's
marked as "Will merge to 'next'", but it's not there yet. Hopefully
you'll see this before it's merged down. Sorry about the delay.

Ævar Arnfjörð Bjarmason (3):
  send-pack.c: move "no refs in common" abort earlier
  fetch: document the --negotiate-only option
  fetch: fix segfault in --negotiate-only without --negotiation-tip=*

 Documentation/config/fetch.txt  |  3 ++-
 Documentation/fetch-options.txt | 13 +++++++++++--
 builtin/fetch.c                 |  3 +++
 send-pack.c                     | 11 ++++++-----
 t/t5702-protocol-v2.sh          | 16 ++++++++++++++++
 5 files changed, 38 insertions(+), 8 deletions(-)

Range-diff against v1:
1:  1cd8b98d3d6 = 1:  10375a6484e send-pack.c: move "no refs in common" abort earlier
2:  7ff734ed70a = 2:  f86f4fc0e6f fetch: document the --negotiate-only option
3:  38930024d95 ! 3:  491d72c35a0 fetch: fix segfault in --negotiate-only without --negotiation-tip=*
    @@ t/t5702-protocol-v2.sh: setup_negotiate_only () {
     +	test_must_fail git -c protocol.version=2 -C client fetch \
     +		--negotiate-only \
     +		origin 2>err.actual &&
    -+	cat err &&
     +	test_cmp err.expect err.actual
     +'
     +