Check if stack is init'ed in call to OCProcess()

OCProcess() returned OC_STACK_OK even when the stack was
not initialized.

Note that even with returning OC_STACK_OK, it was
effectively a no-op as all the other calls in OCProcess() checked for
initialization.

Change-Id: I84423f19390ae840e785e340bc458a5b41b0795a
Signed-off-by: Mandeep Shetty <mandeep.shetty@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/16589Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>

resource/csdk/stack/src/ocstack.c

@@ -3187,6 +3187,10 @@ exit:
 
 OCStackResult OCProcess()
 {
+    if (stackState == OC_STACK_UNINITIALIZED)
+    {
+        return OC_STACK_ERROR;
+    }
 #ifdef WITH_PRESENCE
     OCProcessPresence();
 #endif