date.c: Fix off by one error in object-header date parsing

It is perfectly OK for a valid decimal integer to begin with '9' but
116eb3a (parse_date(): allow ancient git-timestamp, 2012-02-02) did
not express the range correctly.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

date.c

@@ -595,7 +595,7 @@ static int match_object_header_date(const char *date, unsigned long *timestamp,
 	unsigned long stamp;
 	int ofs;
 
-	if (*date < '0' || '9' <= *date)
+	if (*date < '0' || '9' < *date)
 		return -1;
 	stamp = strtoul(date, &end, 10);
 	if (*end != ' ' || stamp == ULONG_MAX || (end[1] != '+' && end[1] != '-'))