Fix some issues of GroupManager
Fix some issues of GroupManager

    - subscribeCollectionPresence()
        - IOT-197 : Handle null parameter
        - IOT-198 : Check that resource has child resource.
    - findCandidateResources()
        - IOT-210 : Handle null parameter

Change-Id: I6961aa776e5883890da226f07d3cfcf64571279c
Signed-off-by: Jack Lee <6641384529c8a1d25686871039cad119df7235e5@samsung.com>
kartben/iotivity,tienfuc/iotivity-democlient-snap,tienfuc/iotivity-democlient-snap,santais/iotivity_1.1,rzr/iotivity,kartben/iotivity,rzr/iotivity,kartben/iotivity,kartben/iotivity,santais/iotivity_1.1.0,WojciechLuczkow/iotivity,iotivity/iotivity,WojciechLuczkow/iotivity,WojciechLuczkow/iotivity,WojciechLuczkow/iotivity,santais/iotivity_1.1.0,kartben/iotivity,rzr/iotivity,iotivity/iotivity,santais/iotivity,santais/iotivity_1.1,santais/iotivity_1.1.0,kartben/iotivity,iotivity/iotivity,WojciechLuczkow/iotivity,kartben/iotivity,iotivity/iotivity,santais/iotivity_1.1,santais/iotivity_1.1,santais/iotivity,WojciechLuczkow/iotivity,santais/iotivity_1.1.0,tienfuc/iotivity-democlient-snap,santais/iotivity_1.1,santais/iotivity_1.1,iotivity/iotivity,santais/iotivity_1.1,WojciechLuczkow/iotivity,tienfuc/iotivity-democlient-snap,tienfuc/iotivity-democlient-snap,rzr/iotivity,iotivity/iotivity,tienfuc/iotivity-democlient-snap,santais/iotivity,tienfuc/iotivity-democlient-snap,kartben/iotivity,santais/iotivity_1.1.0,rzr/iotivity,santais/iotivity,iotivity/iotivity,tienfuc/iotivity-democlient-snap,WojciechLuczkow/iotivity,santais/iotivity_1.1.0,tienfuc/iotivity-democlient-snap,santais/iotivity,rzr/iotivity,iotivity/iotivity,santais/iotivity_1.1.0,santais/iotivity_1.1,santais/iotivity,santais/iotivity,rzr/iotivity,tienfuc/iotivity-democlient-snap