Merge branch 'jt/avoid-lazy-fetch-commits'

Even in a repository with promisor remote, it is useless to
attempt to lazily attempt fetching an object that is expected to be
commit, because no "filter" mode omits commit objects.  Take
advantage of this assumption to fail fast on errors.

* jt/avoid-lazy-fetch-commits:
  commit: don't lazy-fetch commits
  object-file: emit corruption errors when detected
  object-file: refactor map_loose_object_1()
  object-file: remove OBJECT_INFO_IGNORE_LOOSE

diff --cc commit.c
Simple merge

diff --cc object-file.c
Simple merge