Fix a callback problem of PrimitiveResource

Fix a callback problem of PrimitiveResource

The problem was calling the callback even after the object for it was gone.
PrimitiveResource is only created with shared_ptr and callbacks are async operations.
When received the response, there is a possibility that no one holds the resource.

Now checks the object is alive before executing the callback.

Change-Id: I07b20d251c2b8544e7d27f354193b53c910d579c
Signed-off-by: coderhyme <jhyo.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1950
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>