randr: check NULL before dereference
randr: check NULL before dereference

Fixes CID 1181926

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