Merge branch 'jt/avoid-prefetch-when-able-in-diff'

"git diff" in a partial clone learned to avoid lazy loading blob objects in more casese when they are not needed. * jt/avoid-prefetch-when-able-in-diff: diff: restrict when prefetching occurs diff: refactor object read diff: make diff_populate_filespec_options struct promisor-remote: accept 0 as oid_nr in function