[FIX] account: bank statement traceback

Steps to reproduce:
1. Go to Accounting
2. Go to Bank -> Operations
3. Select one of the lines
4. Try to create a statement
5. Traceback

Cause of the issue:
active_ids can be None

opw-3419257

closes odoo/odoo#129078

X-original-commit: 4af42cc815a50d29ba59c1f33703760e671b296c
Signed-off-by: Andrea Grazioso (agr) <agr@odoo.com>
Signed-off-by: Antoine Demany (ande) <ande@odoo.com>

addons/account/models/account_bank_statement.py

@@ -261,7 +261,7 @@ class AccountBankStatement(models.Model):
         if 'line_ids' not in fields_list:
             return defaults
 
-        active_ids = self._context.get('active_ids')
+        active_ids = self._context.get('active_ids', [])
         context_split_line_id = self._context.get('split_line_id')
         context_st_line_id = self._context.get('st_line_id')
         lines = None