s3:lib:wins fix a compile warning on Ubuntu 18.04

s3:lib:wins fix a compile warning on Ubuntu 18.04

gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1) with -O2 puts up a warning here:
../../source3/lib/wins_srv.c: In function ‘wins_srv_tags’:
../../source3/lib/wins_srv.c:235:3: error: assuming signed overflow does not
occur when simplifying conditional to constant [-Werror=strict-overflow]
   for (j=0;j<count;j++) {
   ^~~
cc1: all warnings being treated as errors

Signed-off-by: Christian Ambach <ambi@samba.org>
Reviewed-by: Uri Simchoni <uri@samba.org>
Autobuild-User(master): Uri Simchoni <uri@samba.org>
Autobuild-Date(master): Wed Oct 23 04:57:09 UTC 2019 on sn-devel-184