Do not fail on calculating max ID when setting sequence on empty group

Since 9fdf4dbd66f2 set_sequence calculates the maximum ID but it may be called
with only 0 if the group is empty.

Closes #14689
(grafted from 70eee4cb081a58572fe9b3a4890bac387c2d3e53)

--HG--
branch : 6.0

tryton/tryton/gui/window/view_form/model/group.py

@@ -358,7 +358,7 @@ class Group(SignalEvent, list):
             cmp = operator.gt
         else:
             cmp = operator.lt
-        max_id = max(0, *(r.id for r in self))
+        max_id = max(0, 0, *(r.id for r in self))
         for record in self:
             # Assume not loaded records are correctly ordered
             # as far as we do not change any previous records.