object-name: explicitly handle OBJ_BAD in show_ambiguous_object()

Amend the "unknown type" handling in the code that displays the ambiguous object list to assert() that we're either going to get the "real" object types we can pass to type_name(), or a -1 (OBJ_BAD) return value from oid_object_info(). See [1] for the current output, and [1] for the commit that added the "unknown type" handling. We are never going to get an "unknown type" in the sense of custom types crafted with "hash-object --literally", since we're not using the OBJECT_INFO_ALLOW_UNKNOWN_TYPE flag. If we manage to otherwise unpack such an object without errors we'll die() in parse_loose_header_extended() called by sort_ambiguous() before we get to show_ambiguous_object(), as is asserted by the test added in the preceding commit. So saying "unknown type" here was always misleading, we really meant to say that we had a failure parsing the object at all, i.e. that we had repository corruption. If the problem is only that it's type is unknown we won't reach this code. So let's emit a generic "[bad object]" instead. As our tests added in the preceding commit show, we'll have emitted various "error" output already in those cases. We should do better in the truly "unknown type" cases, which we'd need to handle if we were passing down the OBJECT_INFO_ALLOW_UNKNOWN_TYPE flag. But let's leave that for some future improvement. In a subsequent commit I'll improve the output we do show, and not having to handle the "unknown type" (as in OBJECT_INFO_ALLOW_UNKNOWN_TYPE) simplifies that change. 1. 5cc044e0257 (get_short_oid: sort ambiguous objects by type, then SHA-1, 2018-05-10) 2. 1ffa26c461 (get_short_sha1: list ambiguous objects on error, 2016-09-26) Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>