Keyguard indication area - owner info fix

There was discrepancy between how null values and empty strings were
treated in KeyguardIndication and KeyguardIndicationController. This
could lead to a crash in systemui. Modify the
KeyguardIndicationController to match the logic in KeyguardIndication.

Bug: 201339576
Test: KeyguardIndicationControllerTest
Change-Id: I8b7b4d7b33b1ee809df17e64347c816f65a50727