elm_list.c: check null as well.
elm_list.c: check null as well.

This fixes coverity CID 1049944 Dereference after null check (FORWARD_NULL).

FlorentRevest/Elementary,rvandegrift/elementary,tasn/elementary,tasn/elementary,rvandegrift/elementary,tasn/elementary,FlorentRevest/Elementary,rvandegrift/elementary,FlorentRevest/Elementary,tasn/elementary,tasn/elementary,rvandegrift/elementary,FlorentRevest/Elementary