[FIX] account_cancel: allow cancel of whole bank statement

This revision is related to 6f355623f0.

The above revision had as goal to not allow the partial cancellation
(line per line) of a confirmed bank statement, as it would
prevent the ability to reconcile the statement, as reconcilling
a confirmed statement it not possible.

Nevertheless, cancelling the whole bank statement should be allowed
(using the `Cancel Statement` button), as this cancel all lines
and re-set the statement in draft.

opw-649864
fixes #8568

addons/account_cancel/models/account_bank_statement.py

@@ -12,12 +12,18 @@ class BankStatement(models.Model):
     def button_draft(self):
         self.state = 'draft'
 
+    @api.multi
+    def button_cancel(self):
+        return super(BankStatement, self.with_context(bank_statement_cancel=True)).button_cancel()
+
+
 class BankStatementLine(models.Model):
     _inherit = 'account.bank.statement.line'
 
     @api.multi
     def cancel(self):
-        for line in self:
-            if line.statement_id.state == 'confirm':
-                raise Warning(_("Please set the bank statement to New before canceling."))
+        if not self.env.context.get('bank_statement_cancel'):
+            for line in self:
+                if line.statement_id.state == 'confirm':
+                    raise Warning(_("Please set the bank statement to New before canceling."))
         return super(BankStatementLine, self).cancel()