Fix set_value of Calendar widget

When saving record with focus on calendar widget (which was changed but without
final proper value), the calendar set it to empty instead of trying to complete
the date.

issue3779
review4551002

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

@@ -48,8 +48,7 @@ class Calendar(WidgetInterface):
         return self.entry.grab_focus()
 
     def set_value(self, record, field):
-        field.set_client(record, self.entry.get_text())
-        return True
+        field.set_client(record, self.get_value())
 
     def get_value(self):
         return self.entry.date_get(set_text=False)