Do not use record in __init__ of form widget

During the initialization of the widget, the view may not yet have a proper
record. But update_img access the record of the view.
Also it is safer for list-form to define the _record before calling super in
case there is an access to record attribute.

issue8616
review285981002

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

@@ -44,8 +44,6 @@ class Image(BinaryMixin, Widget):
 
         self._readonly = False
 
-        self.update_img()
-
     @property
     def filters(self):
         filters = super(Image, self).filters

tryton/gui/window/view_form/view/list_form.py

@@ -10,8 +10,8 @@ from .form import ViewForm
 class ListBoxViewForm(ViewForm):
 
     def __init__(self, view_id, screen, xml):
-        super().__init__(view_id, screen, xml)
         self._record = None
+        super().__init__(view_id, screen, xml)
         self.scroll.set_policy(Gtk.PolicyType.NEVER, Gtk.PolicyType.NEVER)
 
     @property