Merge branch 'jk/has-sha1-file-retry-packed'

When an object is not found after checking the packfiles and then
loose object directory, read_sha1_file() re-checks the packfiles to
prevent racing with a concurrent repacker; teach the same logic to
has_sha1_file().

* jk/has-sha1-file-retry-packed:
has_sha1_file: re-check pack directory before giving up

diff --cc sha1_file.c
Simple merge