Fix the failing PreferenceControllerContractTest

In FaceSettings.SearchIndexProvider's createPreferenceControllers
method, we need to check isAvailable() before trying to create the
controllers.

Bug: 127852616
Test: runtest --path ./tests/unit/src/com/android/settings/core/PreferenceControllerContractTest.java
Change-Id: Ib05ba05b8752583eeda61ded78f08f7998d48ba7
1 file changed