Correct some defects detected by Static Code Analysis Tool in things manager

Correct some defects detected by Static Code Analysis Tool in things manager

After running Static Code Analysis Tool(Svace) for things manager codes, some defects have been
detected. Most of the defects are about null pointer handling and variable
initialization. This patchset is for covering these defects.

Change-Id: I97c3a58f08576ef50b636e52027311e7e9e1d04c
Signed-off-by: Jihun Ha <jihun.ha@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4465
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>