Only enable overlay where package is installed

We cannot try to enable icon overlay on managed users because neither
launcher nor the wallpaper picker is installed on managed profiles.
Trying to do so will result in a SecurityException.

Fixes: 180461062
Test: manual
Test: atest ThemeOverlayApplierTest ThemeOverlayControllerTest
Change-Id: I25a07f7a6aa41b6c92c8928091219c4b0fb22770