netfilter: xt_CT: fix wrong checking in the timeout assignment path

The current checking always succeeded. We have to check the first
character of the string to check that it's empty, thus, skipping
the timeout path.

This fixes the use of the CT target without the timeout option.
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_CT.c

@@ -227,7 +227,7 @@ static int xt_ct_tg_check_v1(const struct xt_tgchk_param *par)
 	}
 
 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
-	if (info->timeout) {
+	if (info->timeout[0]) {
 		typeof(nf_ct_timeout_find_get_hook) timeout_find_get;
 		struct nf_conn_timeout *timeout_ext;