Adding rail guard to dispatch's event param

[Chopinsky]

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

When event packet received by onevent doesn't contain a valid array as the value of the data property, the subsequent call to dispatch will cause a TypeError, because the apply call on emit would expect the 2nd parameter to be an array type.

New behaviour

Now if event packet's data property is not already an array, we will convert it to an array before passing it to the apply call, to avoid the TypeError exception on rare occurrence of the problem as raised in issue #3139.

Other information (e.g. related issues)

There seem to be quite a few other places that would use a similar array type check in socket.js, but would rather hold off on updating all these places until further reporting of the TypeError exceptions.

[grajagandev]

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[darrachequesne]

Closed by socketio/socket.io-parser#83