Unable to set Scene directory if scene directory is invalid

[Peregrine05]

If the scene directory is invalid, then changing it within Chunky is not possible. Attempting to open the scene directory picker dialog simply results in an exception, visible in the debug log, essentially saying that the directory path is invalid and cannot be opened (and thus cannot even be changed). The only way to change it is to close Chunky, manually edit the chunky.json to point to a valid directory, and then reopen Chunky. This will always result in unsaved work being lost.