Register fd handler when the client only sets the lang_cb

Register fd handler when the client only sets the lang_cb

- Issue:
Language changes callback is not invoked except by the setting client.

- Solution:
Previous code does not register inotify fd handler when the clients only
set langauge changed callback. The callback needs fd handler
registeration because the callback is called by fd handler. So this
patch adds code to register the fd handler. Through this patch, the
language changd callback will be invoked even if the client is not the
setting client.

Change-Id: I503a5097f7727721292974bd1dc2919401e17593
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>