Crash in OCProcessPresence (#298)

Crash in OCProcessPresence (#298)

* [CONPRO-1285]Crash in OCProcessPresence

There is a issue after freeing the clientcb
we are again accessing it.It can possibly crash.

So, to avoid this scenario we are using LL_FOREACH_SAFE
to iterate the list

Signed-off-by: agrkush <kush.agrawal@samsung.com>
* Update ocstack.c

https://github.sec.samsung.net/RS7-IOTIVITY/IoTivity/pull/298
(cherry picked from commit 578c6918d40d5bded028266ceb3a4aaf68d33623)

Change-Id: Id514a242e34d7a20df2845c09a757b3d26c9604a
Signed-off-by: Amit KS <amit.s12@samsung.com>