Wait for lazy join to complete when getting current state (#12872)

changelog.d/12872.misc

synapse/events/third_party_rules.py

synapse/federation/federation_server.py

synapse/handlers/device.py

synapse/handlers/directory.py

synapse/handlers/federation.py

synapse/handlers/message.py

synapse/handlers/presence.py

synapse/handlers/register.py

synapse/handlers/room.py

synapse/handlers/room_list.py

synapse/handlers/room_member.py

synapse/handlers/room_summary.py

synapse/handlers/stats.py

synapse/handlers/sync.py

synapse/handlers/user_directory.py

synapse/module_api/__init__.py

synapse/push/mailer.py

synapse/rest/admin/rooms.py

synapse/storage/_base.py