fetch-pack: buffer object-format with other args

In send_fetch_request(), "object-format" is written directly to the file
descriptor, as opposed to the other arguments, which are buffered.
Buffer "object-format" as well. "object-format" must be buffered; in
particular, it must appear after "command=fetch" in the request.

This divergence was introduced in 4b831208bb ("fetch-pack: parse and
advertise the object-format capability", 2020-05-27), perhaps as an
oversight (the surrounding code at the point of this commit has already
been using a request buffer.)

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fetch-pack.c

@@ -1210,7 +1210,7 @@ static int send_fetch_request(struct fetch_negotiator *negotiator, int fd_out,
 		if (hash_algo_by_ptr(the_hash_algo) != hash_algo)
 			die(_("mismatched algorithms: client %s; server %s"),
 			    the_hash_algo->name, hash_name);
-		packet_write_fmt(fd_out, "object-format=%s", the_hash_algo->name);
+		packet_buf_write(&req_buf, "object-format=%s", the_hash_algo->name);
 	} else if (hash_algo_by_ptr(the_hash_algo) != GIT_HASH_SHA1) {
 		die(_("the server does not support algorithm '%s'"),
 		    the_hash_algo->name);