calling mContext.unregisterReceiver on an unregistered broadcast receiver will result in an exception. To make the SubscriptionsChangeListener safe from this kind of error, add a check to see whether start has been called before implementing stop's functionality. Bug: 184662284 Bug: 184521296 Test: atest -c SettingsUnitTests Change-Id: Ie901ac6d89f954749793e95923a4a1b1945b9999