Don't complain if /make_join response lacks 'prev_state' list (SYN-517)
Don't complain if /make_join response lacks 'prev_state' list (SYN-517)

iot-factory/synapse,iot-factory/synapse,iot-factory/synapse,matrix-org/synapse,matrix-org/synapse,TribeMedia/synapse,TribeMedia/synapse,iot-factory/synapse,matrix-org/synapse,TribeMedia/synapse,TribeMedia/synapse,TribeMedia/synapse,matrix-org/synapse,matrix-org/synapse,iot-factory/synapse,matrix-org/synapse