cynara: add exception code for cynara_session_id retriving

cynara: add exception code for cynara_session_id retriving

If client exit as soon as  async call, cynara_session_from_pid return null.
cynara_session_from_pid checks /proc/pid to verify client id.

===== reproduce =====
su - owner

dbus-send  --type=method_call  --system --dest=org.tizen.system.deviced  /Org/Tizen/System/DeviceD/Display  org.tizen.system.deviced.display.CustomBrightness
=====================

Signed-off-by: INSUN PYO <insun.pyo@samsung.com>
Change-Id: Ic313e9d4f9531135865824d8512b9eb1ac6f4c9e