Fix NPE in loading group items

Bug 31182164

Change-Id: I194130c0f2ecfaab3dd789aa891015a94115d93d
diff --git a/src/com/android/contacts/group/GroupsFragment.java b/src/com/android/contacts/group/GroupsFragment.java
index be1b44a..32a6900 100644
--- a/src/com/android/contacts/group/GroupsFragment.java
+++ b/src/com/android/contacts/group/GroupsFragment.java
@@ -57,6 +57,9 @@
 
                 @Override
                 public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
+                    if (data == null) {
+                        return;
+                    }
                     mGroupListItems.clear();
                     for (int i = 0; i < data.getCount(); i++) {
                         if (data.moveToNext()) {