adjust: Fix some bad behavior when unlocked files use URL keys.

adjust: Fix some bad behavior when unlocked files use URL keys.

This avoids the smudge --clean filter failing on the URL keys.

git checkout runs the post-checkout hook, which runs smudge --update.
That populates all the pointer files, but it neglected to store their inode
caches in the keys db. With that done, and the keys db flushed before
smudge --clean gets run (by restagePointerFile), the isUnmodifiedCheap
check can tell the file is not modified, so will not try to re-ingest it,
which does not work with URL keys because they do not support genKey.

It also seems possible that the isUnmodifiedCheap was also failing for
non-URL keys, which would cause them to be re-ingested, leading to a lot of
extra work. I have not verified that, but don't see why it wouldn't have
happened. So this probably also speeds up checking out adjusted branches.

This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.