[CIFS] allow cifs_calc_signature2 to deal with a zero length iovec

Currently, cifs_calc_signature2 errors out if it gets a zero-length
iovec. Fix it to silently continue in that case.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsencrypt.c

@@ -99,11 +99,12 @@ static int cifs_calc_signature2(const struct kvec *iov, int n_vec,
 	MD5Init(&context);
 	MD5Update(&context, (char *)&key->data, key->len);
 	for (i = 0; i < n_vec; i++) {
+		if (iov[i].iov_len == 0)
+			continue;
 		if (iov[i].iov_base == NULL) {
 			cERROR(1, ("null iovec entry"));
 			return -EIO;
-		} else if (iov[i].iov_len == 0)
-			break; /* bail out if we are sent nothing to sign */
+		}
 		/* The first entry includes a length field (which does not get
 		   signed that occupies the first 4 bytes before the header */
 		if (i == 0) {