Do not throw an exception if there's no application key to be decrypted

Bug: 73287131
Test: adb shell am instrument -w -e package \
com.android.server.locksettings.recoverablekeystore \
com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner
Change-Id: I17fd94a975312abf9b93080318b7c16a4d388237