fsck: don't hard die on invalid object types

Change the error fsck emits on invalid object types, such as: $ git hash-object --stdin -w -t garbage --literally </dev/null <OID> From the very ungraceful error of: $ git fsck fatal: invalid object type $ To: $ git fsck error: <OID>: object is of unknown type 'garbage': <OID_PATH> [ other fsck output ] We'll still exit with non-zero, but now we'll finish the rest of the traversal. The tests that's being added here asserts that we'll still complain about other fsck issues (e.g. an unrelated dangling blob). To do this we need to pass down the "OBJECT_INFO_ALLOW_UNKNOWN_TYPE" flag from read_loose_object() through to parse_loose_header(). Since the read_loose_object() function is only used in builtin/fsck.c we can simply change it to accept a "struct object_info" (which contains the OBJECT_INFO_ALLOW_UNKNOWN_TYPE in its flags). See f6371f92104 (sha1_file: add read_loose_object() function, 2017-01-13) for the introduction of read_loose_object(). Since we'll need a "struct strbuf" to hold the "type_name" let's pass it to the for_each_loose_file_in_objdir() callback to avoid allocating a new one for each loose object in the iteration. It also makes the memory management simpler than sticking it in fsck_loose() itself, as we'll only need to strbuf_reset() it, with no need to do a strbuf_release() before each "return". Before this commit we'd never check the "type" if read_loose_object() failed, but now we do. We therefore need to initialize it to OBJ_NONE to be able to tell the difference between e.g. its unpack_loose_header() having failed, and us getting past that and into parse_loose_header(). Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>