Fix NPE in CtsSimPhoneBookTestCases

SubscriptionManager.getActiveSubscriptionInfoList can return null and
this is causing pretty much all the tests to fail in a test rule on
some devices (e.g. MTK keystone).

Bug: 271452323
Test: make CtsSimPhonebookProviderTestCases

Change-Id: Ic3442c7df3f822ad9c28113491c061d7052d4821
1 file changed