Bugfix: Add null safety when accessing icon database for main activities for...

Bugfix: Add null safety when accessing icon database for main activities for LoaderTask `loadAllApps`.

Test: verified bugfixes locally.
Bug: 329145005
Flag: NA
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:3a6318ab5e2dee0b85c3270467477854301497a1)
Merged-In: I9f3145390d0596e55229d7dda08a4a3034d75f31
Change-Id: I9f3145390d0596e55229d7dda08a4a3034d75f31