NSRangeException when selecting a row on in the tree detail view

https://rollbar.com/Azavea/OpenTreeMap/items/2376

Version 2.4.0 of the app

```
 NSRangeException: *** -[__NSArrayM objectAtIndex:]: index 4 beyond bounds [0 .. 1]
```

```
OpenTreeMap "OTMTreeDetailViewController.m" line 1004 in -[OTMTreeDetailViewController tableView:didSelectRowAtIndexPath:]
```