Make thread safe codes

Make thread safe codes

The rpc_port_stub_h handle destroys in the main thread. The rpc-port
releases the handle using g_idle_add_full(). Before, the idler is added,
the Ignore() method is called to set nullptr to the event listener.
While calling the callback function, the rpc-port checks whether
the event listener is nullptr or not. If it's nullptr, the callback function
will be returned immediately.

Change-Id: I7728552c38173c548c07ce52c1339c6da9c4b29b
Signed-off-by: Hwankyu Jhun <h.jhun@samsung.com>