Messaging: Finish after no more contacts are blocked

The view doesn't have a "no items available" element and it doesn't
make sense to have one since the menu item is only visible once a contact
is blocked - so after removing the last blocked contact, simply return
back to the conversation list

Change-Id: I3372e26361f6919502cac6fd27ae849d559a4c05

src/com/android/messaging/ui/BlockedParticipantsFragment.java

@@ -75,6 +75,7 @@ public class BlockedParticipantsFragment extends Fragment
      * An adapter to display ParticipantListItemView based on ParticipantData.
      */
     private class BlockedParticipantListAdapter extends CursorAdapter {
+
         public BlockedParticipantListAdapter(final Context context, final Cursor cursor) {
             super(context, cursor, 0);
         }
@@ -96,5 +97,8 @@ public class BlockedParticipantsFragment extends Fragment
     @Override
     public void onBlockedParticipantsCursorUpdated(Cursor cursor) {
         mAdapter.swapCursor(cursor);
+        if (mAdapter.getCount() == 0) {
+            requireActivity().finish();
+        }
     }
 }