An odd request can crash the process when `restify.pre.sanitizePath()` is used

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Restify Version: 11.1.0
Node.js Version: 16, 18, 20

Expected behaviour

Restify should do its best to not crash when weird/unexpected requests are received. It should either return a standard error (e.g. if the method or route is not supported) or invoke the route handler.

Actual behaviour

1. Use normal server.pre(restify.pre.sanitizePath()) middleware

2. Send odd request via curl e.g. curl http://localhost:3000//

3. The Node process running the restify server will crash with this error:

   /Users/abg/git/nexdrew/github/restify-repro/node_modules/assert-plus/assert.js:22
       throw new assert.AssertionError({
       ^
   
   AssertionError [ERR_ASSERTION]: pathname (string) is required
       at RouterRegistryRadix.lookup (/Users/abg/git/nexdrew/github/restify-repro/node_modules/restify/lib/routerRegistryRadix.js:97:12)
       at Router.lookup (/Users/abg/git/nexdrew/github/restify-repro/node_modules/restify/lib/router.js:76:40)
       at Server._runRoute (/Users/abg/git/nexdrew/github/restify-repro/node_modules/restify/lib/server.js:1119:36)
       at Server._afterPre (/Users/abg/git/nexdrew/github/restify-repro/node_modules/restify/lib/server.js:1101:10)
       at preChainDone (/Users/abg/git/nexdrew/github/restify-repro/node_modules/restify/lib/server.js:1069:14)
       at nextTick (/Users/abg/git/nexdrew/github/restify-repro/node_modules/restify/lib/chain.js:145:24)
       at process.processTicksAndRejections (node:internal/process/task_queues:77:11) {
     generatedMessage: false,
     code: 'ERR_ASSERTION',
     actual: 'object',
     expected: 'string',
     operator: '==='
   }
   

Repro case

Please see https://github.com/nexdrew/restify-repro-1959

It includes code and instructions to reproduce the error, and it also contains possible workarounds.

Cause

This issue overlaps with https://github.com/restify/node-restify/issues/1953. The reason I created it as a separate issue is to consider not only a fix to the prePath logic but also to consider handling an empty pathname in the default Router for whatever reason it might occur.

1. Using server.pre(restify.pre.sanitizePath()) strips multiple slashes to an empty string (as stated in #1953)
2. The default router.lookup(req, res) doesn't expect req.getUrl().pathname to be null and doesn't gracefully handle any assertion errors that it might cause

Are you willing and able to fix this?

Yes, I plan to open a PR that includes code changes for both of the workarounds demonstrated in the repro case.

Start with lib/plugins/pre/prePath.js and lib/router.js, following the repro case at restify-repro-1959 with server.pre(restify.pre.sanitizePath()) and curl http://localhost:3000//. Trace how the empty pathname reaches Router.lookup and verify that the process no longer crashes, while the request receives a standard error or reaches its route handler.