bugfix: unref client when removing from exec if exec is deleted
bugfix: unref client when removing from exec if exec is deleted

fixes a race condition where client would never be freed when closing lots of windows simultaneously

rvandegrift/e,rvandegrift/e,rvandegrift/e,tasn/enlightenment,FlorentRevest/Enlightenment,tasn/enlightenment,FlorentRevest/Enlightenment,tizenorg/platform.upstream.enlightenment,tasn/enlightenment,tizenorg/platform.upstream.enlightenment,FlorentRevest/Enlightenment,tizenorg/platform.upstream.enlightenment