eet: add NULL check to eet_connection_empty API to avoid segfault

eet: add NULL check to eet_connection_empty API to avoid segfault

Summary: porting of patch from upstream

commit 0b6e04d94fc3ff6447b6fbf0fcdbdd8b6958e621
Author: Artem Popov <artem.popov@samsung.com>
Date:   Wed Nov 16 15:30:29 2016 -0800

    eet: add NULL-check to eet_connection_empty API to avoid segfault

    @fix

    Summary:
    Only eet_connection_empty hasn't checking on NULL and try to read from field of object.
    Add NULL-check for connection and return result of empty connection.

    Reviewers: jpeg, cedric, myoungwoon

    Subscribers: t.naumenko, NikaWhite

    Differential Revision: https://phab.enlightenment.org/D4399

    Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>
Change-Id: I90113cfa41635f35a6c6ef6d1e1497841f484ce7
Signed-off-by: Prateek Thakur <prateek.th@samsung.com>