[FIX] hr_expense: unlink posted expense

Steps to reproduce:

- Create one (or several) expense lines
- Submit them to the manager (create the expense sheet)
- Approve the sheet and post the entries
- Delete the created and posted sheet

Bug:
- The expense is deleted but the accounting entries are still in the database
- The expense lines are in "To submit" and you can submit to manager again and
generate a new report and therefore new accounting entries...

Fix:
It is not allowed to delete posted expense.

opw:692323

addons/hr_expense/i18n/hr_expense.pot

@@ -1249,6 +1249,12 @@ msgid "You can setup a generic email alias to create\n"
 "                                    in the mail subject to set it on the expense too."
 msgstr ""
 
+#. module: hr_expense
+#: code:addons/hr_expense/models/hr_expense.py:421
+#, python-format
+msgid "You cannot delete a posted expense."
+msgstr ""
+
 #. module: hr_expense
 #: code:addons/hr_expense/models/hr_expense.py:105
 #, python-format

addons/hr_expense/models/hr_expense.py

@@ -417,6 +417,13 @@ class HrExpenseSheet(models.Model):
             self._add_followers()
         return res
 
+    @api.multi
+    def unlink(self):
+        for expense in self:
+            if expense.state == "post":
+                raise UserError(_("You cannot delete a posted expense."))
+        super(HrExpenseSheet, self).unlink()
+
     @api.multi
     def set_to_paid(self):
         self.write({'state': 'done'})