fix crash when access pager_config which is null.
fix crash when access pager_config which is null.

Summary:
crash was happend when user do logout the enlightenment with pager16.
pager_config was freed in e_modapi_shutdown(),
but after that, there was accessing pager_config again in _gc_shutdown() by called gadman_shutdown().

Reviewers: zmike, raster, cedric, seoz

CC: cedric

Differential Revision: https://phab.enlightenment.org/D694

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