Fix UserUpdate not working for typing updates

The code to deal with the right chat action was there,
but the updates that could trigger that code path were
never checked.

telethon/events/userupdate.py

@@ -14,6 +14,14 @@ class UserUpdate(EventBuilder):
         if isinstance(update, types.UpdateUserStatus):
             event = cls.Event(update.user_id,
                               status=update.status)
+        elif isinstance(update, types.UpdateChatUserTyping):
+            # Unfortunately, we can't know whether `chat_id`'s type
+            event = cls.Event(update.user_id,
+                              chat_id=update.chat_id,
+                              typing=update.action)
+        elif isinstance(update, types.UpdateUserTyping):
+            event = cls.Event(update.user_id,
+                              typing=update.action)
         else:
             return
 
@@ -83,9 +91,13 @@ class UserUpdate(EventBuilder):
             contact (`bool`):
                 ``True`` if what's being uploaded (selected) is a contact.
         """
-        def __init__(self, user_id, *, status=None, typing=None):
+        def __init__(self, user_id, *, status=None, chat_id=None, typing=None):
             super().__init__(types.PeerUser(user_id))
 
+            # TODO This should be passed to init, not here
+            # But we need to know the type beforehand
+            self.chat_id = chat_id
+
             self.online = None if status is None else \
                 isinstance(status, types.UserStatusOnline)