Re: [PATCH v2 13/21] packed_ref_cache: keep the `packed-refs` file mmapped if possible

Michael Haggerty [off-list ref] writes:

quoted

+	struct stat st;
+	size_t size, bytes_read;

Coverity helpfully pointed out that `bytes_read` has to be signed:
`ssize_t`. I'll fix that in the next round after waiting for other comments.

Thanks.  

The macOS build at Travis also was also upset about it, so I'd
tentatively queue a trivial squash on top.