DarkUIPreferenceController null exception

The DarkUIPreferenceController doesnt need to show dialog in all cases
we added a null check for mFragment

Fixes: 144899194
Test: atest DarkUIPreferenceControllerTest
Change-Id: Ia5ed89bd46f28f4b92d955911223f9157e55c622
(cherry picked from commit c49f266af0f834ef6db1d53fab80ab8fbfcbb382)
1 file changed