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