Fix key collision for error message in invoice with purchase module

sale.py

@@ -1623,8 +1623,8 @@ class Invoice(ModelSQL, ModelView):
         self._error_messages.update({
             'delete_sale_invoice': 'You can not delete invoices ' \
                     'that come from a sale!',
-            'reset_invoice': 'You cannot reset to draft an invoice '\
-                'generated by a sale.',
+            'reset_invoice_sale': 'You cannot reset to draft ' \
+                    'an invoice generated by a sale.',
             })
 
     def button_draft(self, cursor, user, ids, context=None):
@@ -1633,7 +1633,7 @@ class Invoice(ModelSQL, ModelView):
             cursor, user, [('invoices', 'in', ids)], context=context)
 
         if sale_ids:
-            self.raise_user_error(cursor, 'reset_invoice')
+            self.raise_user_error(cursor, 'reset_invoice_sale')
 
         return super(Invoice, self).button_draft(
             cursor, user, ids, context=context)