[Telephony Helper] Fix telephony plugin while no SIM card inserted

On my Nokia 8, no SIM card means that there is no subscription info, which will lead subscription info list a null pointer. SMS synchronization will fail here(NullPointerException at TelephonyHelper.java line 99):

List<SubscriptionInfo> subscriptionInfos = subscriptionManager.getActiveSubscriptionInfoList();
> List<String> phoneNumbers = new ArrayList<>(subscriptionInfos.size());
for (SubscriptionInfo info : subscriptionInfos) {
    phoneNumbers.add(info.getNumber());
}

where subscriptionInfos is null.

Not filed at Bugzilla, I found it during the test of MR 158 - [SMS Helper] Use simple=true parameter for fetching the list of all conversations.