Some notes:
- Replaced msgpack_unpacker usage with regular xmalloc’ed buffer. Also since
msgpack_unpack_next (as well as msgpack_unpacker_next) is not ever going to
return MSGPACK_UNPACK_EXTRA_BYTES this condition was checked manually.
Function that does return this status is msgpack_unpack, but it is marked as
obsolete.
- Zero type is checked prior to main switch in shada_read_next_item because
otherwise check would be skipped.
- Zeroing entry at the start of shada_read_next_item makes it safer.
- dedent('') does not work.
- v:oldfiles list is only replaced with bang, if it is NULL or empty.
