Stability fixes for PreferenceFragments.

Unregister the click listener as early as possible, so that clicks
don't get delivered after the activity is detached.

Bug: 4599586

This should also fix: 4603030, 4601105, 4598715, 4598712.

Change-Id: I7bcff719bed14ea61b482bd6d29ae1fa5e322e41