Force display of Many2Many screen after edition

Since changeset 0c2f313bf62d, the cancel of the record is not enough to refresh
the display of the edited record in the Many2Many list view. So a display call
must be triggered to clear the CellCache.

issue4391
review6721002

tryton/gui/window/view_form/view/form_gtk/many2many.py

@@ -190,6 +190,8 @@ class Many2Many(Widget):
                 screen.current_record.save()
                 # Force a reload on next display
                 self.screen.current_record.cancel()
+                # Force a display to clear the CellCache
+                self.screen.display()
         WinForm(screen, callback)
 
     def _readonly_set(self, value):