upload-pack: keep poll(2)'s timeout to -1

Keep poll's timeout at -1 when uploadpack.keepalive = 0, instead of
setting it to -1000, since some pedantic old systems (eg HP-UX) and
the gnulib compat/poll will treat only -1 as the valid value for
an infinite timeout.

Signed-off-by: Edward Thomson <ethomson@microsoft.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

upload-pack.c

@@ -158,7 +158,9 @@ static void create_pack_file(void)
 		if (!pollsize)
 			break;
 
-		ret = poll(pfd, pollsize, 1000 * keepalive);
+		ret = poll(pfd, pollsize,
+			keepalive < 0 ? -1 : 1000 * keepalive);
+
 		if (ret < 0) {
 			if (errno != EINTR) {
 				error("poll failed, resuming: %s",