object-name: make get_oid quietly return an error

object-name: make get_oid quietly return an error

A reasonable person looking at the signature and usage of get_oid and
friends might conclude that in the event of an error, it always returns
-1.  However, this is not the case.  Instead, get_oid_basic dies if we
go too far back into the history of a reflog (or, when quiet, simply
exits).

This is not especially useful, since in many cases, we might want to
handle this error differently.  Let's add a flag here to make it just
return -1 like elsewhere in these code paths.

Note that we cannot make this behavior the default, since we have many
other codepaths that rely on the existing behavior, including in tests.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>