send-pack.c: move "no refs in common" abort earlier

send-pack.c: move "no refs in common" abort earlier

Move the early return if we have no remote refs in send_pack()
earlier.

When this was added in 4c353e890c0 (Warn when send-pack does nothing,
2005-12-04) one of the first things we'd do was to abort, but as of
cfee10a773b (send-pack/receive-pack: allow errors to be reported back
to pusher., 2005-12-25) we've added numerous server_supports()
conditions that are acted on later in the function, that won't be used
if we don't have remote refs.

Then as of 477673d6f39 (send-pack: support push negotiation,
2021-05-04) we started doing even more work on the assumption that we
had some remote refs to feed to --negotiation-tip=* options.

We only hit this condition if we have nothing to push, so we don't
need to consider "push.negotiate" etc. only to do nothing with that
information.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>