DeskClock: Fix FAB not being shown everytime

* The getTimer() method returns null when we call getFabTargetVisibility()
  before the onCreateView method gets called, resulting in the FAB not
  being shown
* A video how to reproduce the issue can be found on the bug report linked
  below
* Fix: Always return the first timer (if one exists) so we can properly
  decide if the FAB needs to be shown

Fixes: https://gitlab.com/LineageOS/issues/android/-/issues/2250
Change-Id: Id16686c729ee41d14c890827dc441e81511c8405