Close last terminal does not recreate a default one

When closing the latest tab or latest terminal ("Close terminal" or "close tab"), should recreate a single terminal tab, for consistency sake.

Not sure if this is linked, but I see an error on Custom command:
```
ERROR Invalid custom command file /home/myuser/.config/guake/custom_command.json. Exception: [Errno 2] Aucun fichier ou dossier de ce type: '/home/myuser/.config/guake/custom_command.json'
Traceback (most recent call last):
File "/usr/local/lib/python3.5/dist-packages/guake/customcommands.py", line 53, in _load_json
with open(file_name) as f:
FileNotFoundError: [Errno 2] Aucun fichier ou dossier de ce type: '/home/myuser/.config/guake/custom_command.json'
```

How to reproduce:
- click on "close tab" when there is only 1 tab left
- from now, close tab and close terminal both does not recreate a fresh tab

it also appears to keep somehow the split handles after "close tab" has been hitted.