Add fallback for preferences theme

When preferenceTheme is not defined in the theme we need to provide a
default fallback.

Bug: 118538324
Test: Tested on the studio side
Change-Id: Ia9e375df6bd64c3f6ad9a1eec954d1c83843bf0d
(cherry picked from commit e66fdb5b0ab241d46f1db26d9b9c7e7712c610f9)
1 file changed