prevent traceback when destroy handler already clean self.instances[account]['online_dialog'] dict. Fixes #5604

improve bigger avatar behaviour in case on_avatar_eventbox_enter_notify_event is called twice (when using unclutter). Fixes #5590

[David Flatz] show transports even if show transports is false when they have unread events. Fixes #5591

add XEP-0184 warning image in textview with an empty text so copy/past don't include a strange char. Fixes #5578