Ensure non null package

Switch most usages of rule.pkg over to rule.getPkg() except for
ones that render Settings UIs, where a null package implies the UI
should be shown differently

Test: atest; trigger DND with a rule created before we started storing pkg
from the creating app rather than inferring it
Fixes: 191827482

Change-Id: I8fce30077d9e457ab0402b913dc551e55de2ee8f