Return error atom according to specification

In stream topology function call. This would
trigger an exception in the frame creation
when the stream was not available because the atom
was unexpected.

Author: acogoluegnes

deps/rabbitmq_stream/src/rabbit_stream_manager.erl

@@ -418,8 +418,10 @@ handle_call({topology, VirtualHost, Stream}, _From, State) ->
                                      #{leader_node => undefined,
                                        replica_nodes => []},
                                      Members)};
-                      _ ->
-                          {error, not_available}
+                      Err ->
+                          rabbit_log:info("Error locating ~tp stream members: ~tp",
+                                          [StreamName, Err]),
+                          {error, stream_not_available}
                   end;
               {error, not_found} ->
                   {error, stream_not_found};