fix middleware initialization

[darrachequesne]

The kind of change this PR does introduce

• a bug fix
• a new feature
• an update to the documentation
• a code change that improves performance
• other

Current behaviour

New behaviour

Fix TypeError: Cannot convert undefined or null to object when a middleware is added before the engine is properly attached.

Other information (e.g. related issues)

Closes #2963.

[ghost]

/data/project/app/node_modules/on-headers/index.js:25
	throw new TypeError('argument res is required')
	^

TypeError: argument res is required
	at onHeaders (/data/project/app/node_modules/on-headers/index.js:25:11)
	at session (/data/project/app/node_modules/express-session/index.js:219:5)
	at Array.<anonymous> (/data/project/app/modules/webserver.js:41:5)
	at run (/data/project/app/node_modules/socket.io/lib/namespace.js:123:11)
	at Namespace.run (/data/project/app/node_modules/socket.io/lib/namespace.js:135:3)
	at Namespace.add (/data/project/app/node_modules/socket.io/lib/namespace.js:163:8)
	at Client.connect (/data/project/app/node_modules/socket.io/lib/client.js:76:20)
	at Server.onconnection (/data/project/app/node_modules/socket.io/lib/index.js:398:10)
	at emitOne (events.js:115:13)
	at Server.emit (events.js:210:7)
error: Forever detected script exited with code: 1
error: Script restart attempt #63

const session = require('express-session');
[..]
const httpsServer = https.createServer(credentials, app).listen(config.server.port);
const io = require('socket.io')(httpsServer);

var sessionMiddleware = session({
    store: new RedisStore({}),
    secret: 'MYSECRET',
    resave: false,
    saveUninitialized: true
});

io.use(function (socket, next) {
    sessionMiddleware(socket.request, socket.request.res, next); //(/data/project/app/modules/webserver.js:41:5)
});

this error occurred the first time after updating from 2.0.2 to 2.0.3 - any ideas?

[ToddAlvord]

Gindu's error occurs for me on any version of v2. I searched for the new location of res and could not find it.
sessionMiddleware( socket.request, {}, next );
The above line works and you still have session data, but you cannot modify or save the session this way.