Fix regression where ShortcutRequest returns no results

There was a subtle bug introduced by ag/9898176 where we now accept
String... shortcutIds. There are a couple calls that don't pass any
id's, which means the shortcut query is doomed to return an empty list.
Instead, we should pass null to match all shortcuts for that package.

Bug: 147831521
Change-Id: I928b6ed23b7e0ad01d95749cabf88ada053bcdd3