New payment slip for v8

```
File "/home/gbaconnier/code/dev/parts/l10n-switzerland/l10n_ch_payment_slip/payment_slip.py", line 218, in _compute_scan_line_list
    account_components[1].rjust(6, '0'),
ValueError: "list index out of range" while evaluating
```
if `get_account_number()` returns an account in the wrong format (no `-` in mine for instance).