Use root user to read sale lines

issue2654
review402001
(transplanted from 226fbbe2d434194e54cbcefcaed11c363430fbf8)

invoice.py

@@ -4,6 +4,7 @@ from decimal import Decimal
 import operator
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.pool import Pool
+from trytond.transaction import Transaction
 
 
 class InvoiceLine(ModelSQL, ModelView):
@@ -66,7 +67,9 @@ class InvoiceLine(ModelSQL, ModelView):
                     for move in purchase_line.moves
                     if move.state == 'done']
         elif line.invoice.type == 'out_invoice':
-            moves = [move for sale_line in line.sale_lines
+            with Transaction().set_user(0, set_context=True):
+                sale_lines = self.browse(line.id).sale_lines
+            moves = [move for sale_line in sale_lines
                     for move in sale_line.moves
                     if move.state == 'done']
         if line.invoice.type == 'in_invoice':