Prevent NPE when GlobalActions items are clicked while the dialog isn't showing.

Unclear what circumstances this can happen in, perhaps a race condition for tapping items rapidly while the phone is under heavy load and running very slowly. Added warning logs in case we need to investigate further.

Test: Automated tests pass, GlobalActionsMenu still works as expected when tapping action items.

Bug: 134514187
Change-Id: I0c50ee02cc54d046a12e56f01d9c129122fbf737