Application accepts null intents causing a crash

Change-Id: Ia7f98f43567f25ae7abc6e5ac7e07323e75d9047
Fixes: 116869239
Test: adb shell am start -n com.android.settings/com.android.settings.Settings\\\$ApnEditorActivity
Test: make RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.network"

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

@@ -231,9 +231,13 @@ public class ApnEditor extends SettingsPreferenceFragment
 
         final Intent intent = getIntent();
         final String action = intent.getAction();
+        if (TextUtils.isEmpty(action)) {
+            finish();
+            return;
+        }
+
         mSubId = intent.getIntExtra(ApnSettings.SUB_ID,
                 SubscriptionManager.INVALID_SUBSCRIPTION_ID);
-
         mReadOnlyApn = false;
         mReadOnlyApnTypes = null;
         mReadOnlyApnFields = null;