Add package install check before adding userId to list.

DocsUi returns null label and badge for profiles that don't have the
com.google.android.documentsui package installed. This change adds a
check to ensure that only profiles with the package installed are added
to the user list, preventing crashes caused by operations on null badges
or labels.

Bug: 387266472
Test: manual
Flag: EXEMPT bugfix
Change-Id: Ia731cb56796bb2a870fe37d642a062980f756c15