[FIX] l10n_id_efaktur: fix the issue of invalid literal base10 in efaktur

If applied, this commit will solve the min-max issues for efaktur.

- invalid literal for int() with base 10: when we enter all characters
string in the min or max it will raise an error like this.

- Error is also raised when the min or max is blank and try to save the
record.

So, I have update the value as 0 if the min value or max value not
generated.

see - https://tinyurl.com/2lx9j2kr



Sentry - 3936020226

closes odoo/odoo#112850

Signed-off-by: William André (wan) <wan@odoo.com>