Fix crash issue when called unsubscribePresence.

Fix crash issue when called unsubscribePresence.

Adding null initialization code.

Change-Id: I2d52b1fa479dd1956f089d202aa01fcc7da09e52
Signed-off-by: Jaehong Jo <jaehong.jo@samsung.com>
Signed-off-by: jihwan.seo <jihwan.seo@samsung.com
Signed-off-by: hyuna0213.jo <hyuna0213.jo@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11069
Reviewed-by: jihwan seo <jihwan.seo@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>