[Settings] Only display backup calling when more than 1 SIM

Backup calling only available when more than 1 SIM available.

Bug: 179802059
Test: on device
Change-Id: I24e5eb9e1a7064c3ea65389fbb00c0ff2a5852ed

src/com/android/settings/network/SubscriptionUtil.java

@@ -70,6 +70,9 @@ public class SubscriptionUtil {
         if (sActiveResultsForTesting != null) {
             return sActiveResultsForTesting;
         }
+        if (manager == null) {
+            return Collections.emptyList();
+        }
         final List<SubscriptionInfo> subscriptions = manager.getActiveSubscriptionInfoList();
         if (subscriptions == null) {
             return new ArrayList<>();