Fix issues shown by cppcheck for wrt-plugins-common

Fix issues shown by cppcheck for wrt-plugins-common

[Issue#] LINUXWRT-124
[Problem] Cppcheck appears some warnings for wrt-plugins-common.
[Cause] Incorrect code.

[Solution] Make some changes.

[Verification] Run cppcheck on wrt-plugins-common (omitting
incorrectStringBooleanError). It would be no warnings.

I used the command:
cppcheck --std=posix --std=c++11 --std=c99 --max-configs=1 --enable=all
"`PKG_CONFIG_LIBDIR="/home/grynkowski/GBS-ROOT/local/scratch.armv7l.0/usr/lib/pkgconfig"
PKG_CONFIG_SYSROOT_DIR="/home/grynkowski/GBS-ROOT/local/scratch.armv7l.0"
pkg-config --cflags-only-I dpl-efl wrt-plugins-types security-client
dpl-event-efl ewebkit2 dpl-wrt-dao-ro dpl-wrt-dao-rw dpl-db-efl
libpcrecpp icu-i18n libxml-2.0 cert-svc-vcore`"
"/home/grynkowski/ngwap/wrt-plugins-common"
--suppress=incorrectStringBooleanError

Change-Id: I8cc6142660c4f2253909c7537cc966a3c027fa6f