External-deleted projects remain in app ("End of input at character 0 of" error)

Steps to reproduce:

1. Delete a project on the server without using the app
2. Open MoneyBuster; it refreshes
3. Error toast appears: "Project sync failed: is the Cospend app activated on the server? org.json.JSONException: End of input at character 0 of"

Cospend app is still activated and server is up. But project is gone. A popup should ask me if the project has been really deleted and if I want to delete the project locally too.