Fix NPE in AudioSwitchPreferenceController

Test: Unit Test to verify nullness
Bug: 338892614
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:7ac80f0a0a69e99ec3603e9157cd5a2b20509e85)
Merged-In: Ic97d1a6269a6d98ffd15a9b512f6ae24ff1c5b5e
Change-Id: Ic97d1a6269a6d98ffd15a9b512f6ae24ff1c5b5e
2 files changed