Fix UP button not working in preference activity

When pressing the UP button in a preference activity, some
implementations call Activity#onBackPressed. In case, predictive back is
enabled, this may not behave correctly. If no back callback is
registered, the activity should be finished in that case.

Bug: 391752210
Flag: EXEMPT bugfix
Test: Manual, i.e. enable predictive back in Dialer app and verify correct UP button behaviour.
Test: CtsPreferenceTestCases
Change-Id: If1a80a4d2c8c7f9e21e0b695059e942ee1f1ce4c