The object lookup machinery has been taught to gracefully recover
when a multi-pack-index points to an owning pack that was removed
during a concurrent geometric repack, and 'git replay' has been
fixed to not segfault when reading such missing objects.
* en/midx-missing-pack-fallback:
packfile: recover when a multi-pack-index names a removed pack
mktree: do not use OBJECT_INFO_QUICK when checking objects
mktree: plug per-tree leak in --batch mode
replay: fail gracefully when a merge input is unreadable
73a4cd73de