Merge branch 'jt/diff-lazy-fetch-submodule-fix'

On-demand object fetching in lazy clone incorrectly tried to fetch
commits from submodule projects, while still working in the
superproject, which has been corrected.

* jt/diff-lazy-fetch-submodule-fix:
  diff: skip GITLINK when lazy fetching missing objs

diff --cc diff.c
Simple merge