pack-objects tests: cover blindspots in stdin handling
Cover blindspots in the testing of stdin handling, including the "!len" condition added in b5d97e6b0a0 (pack-objects: run rev-list equivalent internally., 2006-09-04). The codepath taken with --revs and read_object_list_from_stdin() acts differently in some of these common cases, let's test for those. The "--stdin --revs" test being added here stresses the combination of --stdin-packs and the revision.c --stdin argument, some of this was covered in a test added in 339bce27f4f (builtin/pack-objects.c: add '--stdin-packs' option, 2021-02-22), but let's make sure that GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS=true keeps erroring out about --stdin, and it isn't picked up by the revision.c API's handling of that option. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>