Fix logic for joining rooms.

server/config/config.example.js

@@ -40,6 +40,10 @@ module.exports =
 	// If false, there is no difference between guests and signed-in
 	// users when joining.
 	requireSignInToAccess : true,
+	// This flag has no effect when requireSignInToAccess is false
+	// When truthy, the room will be open to all users when the first
+	// authenticated user has already joined the room.
+	activateOnHostJoin    : true,
 	// Mediasoup settings
 	mediasoup             :
 	{