remote: give up after 256 failures to find a common object

This avoids sending our whole history bit by bit to the remote in cases
where there is no common history, just to give up in the end.

The number comes from the canonical implementation.

src/transports/smart_protocol.c

@@ -279,19 +279,20 @@ int git_smart__negotiate_fetch(git_transport *transport, git_repository *repo, c
 	unsigned int i;
 	git_oid oid;
 
-	/* No own logic, do our thing */
 	if ((error = git_pkt_buffer_wants(refs, count, &t->caps, &data)) < 0)
 		return error;
 
 	if ((error = fetch_setup_walk(&walk, repo)) < 0)
 		goto on_error;
+
 	/*
-	 * We don't support any kind of ACK extensions, so the negotiation
-	 * boils down to sending what we have and listening for an ACK
-	 * every once in a while.
+	 * Our support for ACK extensions is simply to parse them. On
+	 * the first ACK we will accept that as enough common
+	 * objects. We give up if we haven't found an answer in the
+	 * first 256 we send.
 	 */
 	i = 0;
-	while (true) {
+	while (i < 256) {
 		error = git_revwalk_next(&oid, walk);
 
 		if (error < 0) {