If a commit is in the commit graph, we would expect the commit to also
be present. So we should use has_object() instead of
repo_has_object_file(), which will help us avoid getting into an endless
loop of lazy fetch.

When we found the commit in the graph in lookup_commit_in_graph(), but
the commit is missing from the repository, we will try
promisor_remote_get_direct() and then enter another loop. While
sometimes it will finally succeed because it cannot fork subprocess,
it has exhausted the local process resources and can be harmful to the
remote service.

Signed-off-by: Han Xin <hanxin.hx@bytedance.com>