Accounts for PackageSetting.pkg == null

In some dev cases and potentially for apps on a removed adoptable
storage device, the targetting packagesetting may have a null package.
This change adds a check for that and treats the app as not queryable.

Fixes: 138658673
Test: atest AppsFilterTest
Change-Id: I1849247d492f3c3bf30c6ea9c3c8696274729f7b