Fix NPE in AddUserWhenLockedPreferenceController.

Set LockPatternUtils in constructor, but allow it to be
overridden for tests.

Bug: 149511500
Test: make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.users.AddUserWhenLockedPreferenceControllerTest"
Change-Id: I4148fec8eea9c76afebe45cc29c2c87775fd3b1e
3 files changed