Fix crashes seen when checking for carrierConfig certificates

1. Do not throw exception when packageName is not found
2. Fix NPE caused by null SubscriptionInfo

Bug: 140122832
Test: Utest and manual test
Change-Id: I686647419896a1780f0697b3ed5d319363675f5f
Merged-In: I686647419896a1780f0697b3ed5d319363675f5f
2 files changed