Fix NPE in streamin policy getters.

If there is a DO but it is not on userId, admin was null.

With this change DO policies set on other users aren't
taken into account, NEARBY_STREAMING_NOT_CONTROLLED_BY_POLICY
is returned.

Fixes: 264761323
Test: atest NearbyNotificationStreamingPolicyTest
Test: atest NearbyAppStreamingPolicyTest
Change-Id: I4562fb44d663a2d590ab92dd66b881b636838910