Exception raised during species selection

[jwalgran]

https://rollbar.com/Azavea/OpenTreeMap/items/2375/

Reported by version 2.4.0

NSInternalInconsistencyException: -[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object 

OpenTreeMap in -[NSDictionary(DecodeKey) setObject:forEncodedKey:] (NSDictionary
OpenTreeMap "OTMTreeDetailViewController.m" line 888 in __54-[OTMTreeDetailViewController prepareForSegue:sender:]_block_invoke
OpenTreeMap "OTMSpeciesTableViewController.m" line 196 in -[OTMSpeciesTableViewController tableView:didSelectRowAtIndexPath:]