hash-object: fix descriptor leak with --literally

In hash_object(), we open a descriptor for each file to hash (whether we
got the filename from the command line or --stdin-paths), but never
close it. For the traditional code path, which feeds the result to
index_fd(), this is OK; it closes the descriptor for us.

But 5ba9a93b39 (hash-object: add --literally option, 2014-09-11) added a
second code path, which does not close the descriptor. There we need to
do so ourselves.

You can see the problem in a clone of git.git like this:

  $ git ls-files -s | grep ^100644 | cut -f2 |
    git hash-object --stdin-paths --literally >/dev/null
  fatal: could not open 'builtin/var.c' for reading: Too many open files

After this patch, it completes successfully. I didn't bother with a
test, as it's a pain to deal with descriptor limits portably, and the
fix is so trivial.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/hash-object.c

@@ -27,6 +27,7 @@ static int hash_literally(struct object_id *oid, int fd, const char *type, unsig
 	else
 		ret = write_object_file_literally(buf.buf, buf.len, type, oid,
 						 flags);
+	close(fd);
 	strbuf_release(&buf);
 	return ret;
 }