Handle null intent in WifiCallingPreferenceController

When intent is null, we will hide wifi calling preference however
its listener might still triggered with null intent.

This CL update controller so it can handle this event inside listener
callback.

Fixes: 135095929
Test: RunSettingsRoboTests
Change-Id: I4c5aba03871f11a2d9f9b4da329c2c2655ff9adb