Deleting a folder containing an open graph does not update the graph window

Steps to reproduce:

1. Download and import the attached "gtk-delete-folder.unitypackage"
2. Open "Basic graph" in the "Repro" folder
3. Delete the "Repro" folder

Actual results: The window still shows the graph

Expected results: The window is empty

Reproducible with versions: 
0.2.0-exp.1 (6.3a4; 6.2b12)

Tested on (OS): MacOS