things-manager: Fix cppcheck issues in TMSampleApp for tizen

things-manager: Fix cppcheck issues in TMSampleApp for tizen

This patch fixes the below issues
reported by cppcheck tool in TMSampleApp dir for tizen.
"(error) Possible null pointer dereference: popup_fields ...."

It is invliad to set the member of popup_field to NULL if
popup_field itself is NULL.
Removed such statements from the code.

Change-Id: Ie1457662cb2727e5bab5e21886db6bece2f356a7
Signed-off-by: Ravi Nanjundappa <nravi.n@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1511
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Harish Marappa <h.marappa@samsung.com>
Reviewed-by: Uze Choi <uzchoi@samsung.com>