netfilter: ftp: Remove the useless dlen==0 condition check in find_pattern

The caller function "help" has already make sure the datalen could not be zero
before invoke find_pattern as a parameter by the following codes

        if (dataoff >= skb->len) {
                pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff,
                         skb->len);
                return NF_ACCEPT;
        }
        datalen = skb->len - dataoff;

And the latter codes "ends_in_nl = (fb_ptr[datalen - 1] == '\n');" use datalen
directly without checking if it is zero.

So it is unneccessary to check it in find_pattern too.
Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_ftp.c

@@ -301,8 +301,6 @@ static int find_pattern(const char *data, size_t dlen,
 	size_t i = plen;
 
 	pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen);
-	if (dlen == 0)
-		return 0;
 
 	if (dlen <= plen) {
 		/* Short packet: try for partial? */