Add req.socket.destroy()

[yus-ham]

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This ensures invocation to req.socket.destroy() won't makes exception thrown as it happen before in my express app

125 |     // cannot actually respond
126 |     if (headersSent(res)) {
127 |       debug('cannot %d after headers sent', status)
128 |       if (req.socket) {
129 |         console.info('finalhandler req.socket:',req.socket)
130 |         req.socket.destroy()
                         ^
TypeError: req.socket.destroy is not a function. (In 'req.socket.destroy()', 'req.socket.destroy' is undefined)
      at <anonymous> (/app/node_modules/finalhandler/index.js:130:20)

[mcollina]

lgtm

[jsumners]

This seems reasonable, but I wonder what the use case is that makes it necessary. This library has been around for a long time without any reports of this being a problem.

Basically, a test has been included to assert that the method exists and doesn't do anything, but there is not a test that shows what is being fixed.