Clear entry when combobox is set to inactive item

GTK doesn't clear the entry when calling set_active with -1.
Complete changeset 112709fa23f4.

issue4298
review13991002

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

@@ -129,6 +129,9 @@ class Reference(Many2One, SelectionMixin, PopdownMixin):
                 active = i
                 break
         self.widget_combo.set_active(active)
+        if active == -1:
+            # When setting no item GTK doesn't clear the entry
+            self.widget_combo.child.set_text('')
 
     def display(self, record, field):
         self.update_selection(record, field)

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

@@ -68,6 +68,8 @@ class Selection(Widget, SelectionMixin, PopdownMixin):
         self.set_popdown(self.selection, self.entry)
         if not field:
             self.entry.set_active(-1)
+            # When setting no item GTK doesn't clear the entry
+            self.entry.child.set_text('')
             return
         super(Selection, self).display(record, field)
         value = field.get(record)