Gracefully ignore items that don't support notifications

PackageUserKey is only meant to be used for items that support
notifications, so when trying to update it for an item that
doesn't, we don't use it to check if the item has notifications.

This fixes a crash that happens when trying to update notifications
for a legacy shortcut, as such a shortcut doesn't have a component
on its intent, which we were trying to use to populate PackageUserKey.

Bug: 34842278
Change-Id: I8c69ccebbf9d93505d5b29ecd25d76c65610ddc4