send-pack: always allocate receive status

send-pack: always allocate receive status

In `receive_status()`, we record the reason why ref updates have been
rejected by the remote via the `remote_status`. But while we allocate
the assigned string when a reason was given, we assign a string constant
when no reason was given.

This has been working fine so far due to two reasons:

  - We don't ever free the refs in git-send-pack(1)'

  - Remotes always give a reason, at least as implemented by Git proper.

Adapt the code to always allocate the receive status string and free the
refs.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>