Handle case when PlatformKey is invalid.

When Platform key is invalidated, all applicatio keys wraped into it
needs to be marked as unrecoverable.
It can happen when user removes screen lock.

Bug: 72443379
Test: adb shell am instrument -w -e package
com.android.server.locksettings.recoverablekeystore
com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner

Change-Id: I7ae257f8fdb4b6abf789887f15b02a2fe370dfb8