Clear tasks and start a new one when we failed to restore a task.

This is to cover a corner case where the targeted activity has been
moved across system updates so Android can't find the targeted activity.

Test: It stops crashing and tasks can still be restored.
Bug: 32178848
Change-Id: I2288b3e8758d2e4f86b61f101aaeb834e1f9b719
1 file changed