Fix error handler in topology.connect

[simllll]

if topology.connect has an error, topology is "overwritten" which leads to an error like:

     Uncaught TypeError: Cannot read property 'close' of undefined
      at topology.connect (node_modules/mongodb/lib/operations/mongo_client_ops.js:412:16)
      at ReplSet.<anonymous> (node_modules/mongodb/lib/topologies/replset.js:364:11)
      at node_modules/mongodb-core/lib/topologies/replset.js:634:14
      at Server.<anonymous> (node_modules/mongodb-core/lib/topologies/replset.js:357:9)
      at node_modules/mongodb-core/lib/topologies/server.js:508:16
      at node_modules/mongodb-core/lib/connection/pool.js:531:18
      at process._tickCallback (internal/process/next_tick.js:61:11)

changing the function parameter to a new name, let's "force close" the old instance.

[vkarpov15]

@simllll @mbroadst I can confirm this fixes an issue that's popping up in the Mongoose tests. I looked into it and it is a minor issue that seems to pop up when you specify the replicaSet option when connecting to a standalone mongod.

const { MongoClient } = require('mongodb');

run().catch(error => console.error(error.stack));

async function run() {
  // Fails with "Cannot read property 'close' of undefined" if localhost:27017 is a standalone
  await MongoClient.connect('mongodb://localhost:27017/test', { replicaSet: 'rs', useNewUrlParser: true });
}

We can work around this for now

[mbroadst]

@vkarpov15 @simllll thanks for catching this! It's strange because it should technically be the same object, but I definitely prefer the enhanced readability. We're working diligently on a fix for the change streams resume issues, so this fix here will likely make it into a patch release this week including that and updated kerberos support.