Gracefully handle null volumes after forgetting.

If a user tells a device to forget a storage volume and then
goes back to the PrivateVolumeForget activity from their Recents, it
attempts to re-initialize itself with a volume that it forgot.

And this makes Settings crash.

By gracefully killing the activity when we try to open
PrivateVolumeForget for a forgotten volume, we avoid this crash.

Change-Id: Ib4e881c10f0c872ce6b268b16a573960230ef99b
Fixes: 34856304
Test: Settings unit test

src/com/android/settings/deviceinfo/PrivateVolumeForget.java

@@ -53,8 +53,18 @@ public class PrivateVolumeForget extends SettingsPreferenceFragment {
             Bundle savedInstanceState) {
         final StorageManager storage = getActivity().getSystemService(StorageManager.class);
         final String fsUuid = getArguments().getString(VolumeRecord.EXTRA_FS_UUID);
+        // Passing null will crash the StorageManager, so let's early exit.
+        if (fsUuid == null) {
+            getActivity().finish();
+            return null;
+        }
         mRecord = storage.findRecordByUuid(fsUuid);
 
+        if (mRecord == null) {
+            getActivity().finish();
+            return null;
+        }
+
         final View view = inflater.inflate(R.layout.storage_internal_forget, container, false);
         final TextView body = (TextView) view.findViewById(R.id.body);
         final Button confirm = (Button) view.findViewById(R.id.confirm);