Doesn't open interface when --pref is given

When a non-existent sketchbook folder is specified, the IDE gives a popup saying "Sketchbook folder disappeared", saying it will revert to the default sketchbook folder. However, instead of doing that, it just quits, without opening up the IDE interface.

To reproduce:

```
arduino --pref sketchbook.path=/nonexistent
```

Start by running the reported `arduino --pref sketchbook.path=/nonexistent` command and trace the startup path that handles the “Sketchbook folder disappeared” popup. Done means the IDE opens its interface after reverting to the default sketchbook folder instead of quitting.

Written by the indexing model from the issue text.