Synchronously call callback when load is cancelled

This prevents the case when controller unbinds and nulls the provider
used by the callback with a slight delay. Callback is ignored when there
is no provider and ControlsController gets stuck in seeding state.

Test: manual with the steps from the comment#18
Test: atest ControlsBindingControllerImplTest
Fixes: 283888863
Change-Id: I5683170b71ad47702c924fbb2df293118937cb37