[Settings] Fix NPE from updating subinfo changed.

- Refactor code to avoid NPE.

Bug: 278721219
Test: make passed
Test: atest MobileDataPreferenceControllerTest passed
Change-Id: I1fe57b8835677335ae9102cfff71451060ea4f78

src/com/android/settings/network/telephony/MobileDataPreferenceController.java

@@ -25,10 +25,10 @@ import android.telephony.TelephonyManager;
 import android.text.TextUtils;
 
 import androidx.annotation.VisibleForTesting;
+import androidx.fragment.app.FragmentManager;
 import androidx.lifecycle.LifecycleObserver;
 import androidx.lifecycle.LifecycleOwner;
 import androidx.lifecycle.OnLifecycleEvent;
-import androidx.fragment.app.FragmentManager;
 import androidx.preference.Preference;
 import androidx.preference.PreferenceScreen;
 import androidx.preference.SwitchPreference;
@@ -232,13 +232,12 @@ public class MobileDataPreferenceController extends TelephonyTogglePreferenceCon
         mSubscriptionInfoEntityList.forEach(entity -> {
             if (entity.getSubId() == mSubId) {
                 mSubscriptionInfoEntity = entity;
+                if (entity.getSubId() == SubscriptionManager.getDefaultDataSubscriptionId()) {
+                    mDefaultSubId = entity.getSubId();
+                }
             }
         });
-        int subId = mSubscriptionInfoEntity.getSubId();
-        if (mSubscriptionInfoEntity != null
-                && subId == SubscriptionManager.getDefaultDataSubscriptionId()) {
-            mDefaultSubId = subId;
-        }
+
         update();
         refreshSummary(mPreference);
     }

tests/unit/src/com/android/settings/network/telephony/MobileDataPreferenceControllerTest.java

@@ -20,7 +20,6 @@ import static com.android.settings.core.BasePreferenceController.AVAILABLE_UNSEA
 
 import static com.google.common.truth.Truth.assertThat;
 
-import static org.mockito.Matchers.anyInt;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.verify;