Fix NPE from ListsFragment crash.

I'm not sure if anyone else is seeing this, but this change didn't
seem like it would be harmful to make. I was running into sadness
because mListsFragment was undefined.

Change-Id: I75712c2cb3626002372ac9b4812c44c2ed74c12f
diff --git a/src/com/android/dialer/DialtactsActivity.java b/src/com/android/dialer/DialtactsActivity.java
index 2bda091..167c131 100644
--- a/src/com/android/dialer/DialtactsActivity.java
+++ b/src/com/android/dialer/DialtactsActivity.java
@@ -410,8 +410,9 @@
         // Add the favorites fragment but only if savedInstanceState is null. Otherwise the
         // fragment manager is responsible for recreating it.
         if (savedInstanceState == null) {
+            mListsFragment = new ListsFragment();
             getFragmentManager().beginTransaction()
-                    .add(R.id.dialtacts_frame, new ListsFragment(), TAG_FAVORITES_FRAGMENT)
+                    .add(R.id.dialtacts_frame, mListsFragment, TAG_FAVORITES_FRAGMENT)
                     .commit();
         } else {
             mSearchQuery = savedInstanceState.getString(KEY_SEARCH_QUERY);