Merge branch 'jk/no-looking-at-dotgit-outside-repo'

Clean up fallouts from recent tightening of the set-up sequence,
where Git barfs when repository information is accessed without
first ensuring that it was started in a repository.

* jk/no-looking-at-dotgit-outside-repo:
test-read-cache: setup git dir
has_sha1_file: don't bother if we are not in a repository

diff --cc sha1_file.c
Simple merge