Don't let NotificationMediaManager cause NPEs

If setUpWithPresenter() hasn't been called on NotificationMediaManager,
it can NPE when serving up APIs.

Long term, we probably need a way to make sure classes which need to bet
set up don't do anything before they get that chance.

Test: open camera, kill sysui, make sure it boots
Change-Id: Idc41bf9aeecda2bcc55c03b4c027c15fbc880a4f
Fixes: 119322135