Handle type state being undefined for very old queues

Field #amqqueue.type_state can be undefined for queues declared on old
RabbitMQ versions before 3.8.0. Ensure `amqqueue:get_type_state/1`
always returns a map according to its type spec to make life of
calling code easier.

Author: gomoripeti

deps/rabbit/src/amqqueue.erl

@@ -464,7 +464,7 @@ set_policy_version(#amqqueue{} = Queue, PV) ->
 % type_state (new in v2)
 
 -spec get_type_state(amqqueue()) -> map().
-get_type_state(#amqqueue{type_state = TState}) ->
+get_type_state(#amqqueue{type_state = TState}) when is_map(TState) ->
     TState;
 get_type_state(_) ->
     #{}.