Noissue - Remove unnecessary typeof checks in lib/matcher.js

In many even if not most cases, `typeof foo == "undefined"` can be replaced with a `!foo` or `foo == null`, both of which are faster.

[Manish Jethani, 2018-06-12 04:50:27]

Patch Set 1

https://codereview.adblockplus.org/29804575/diff/29804576/lib/matcher.js
File lib/matcher.js (right):

https://codereview.adblockplus.org/29804575/diff/29804576/lib/matcher.js#newc...
lib/matcher.js:87: if (keyword == null)
keyword can be an empty string, so we must check against null here.

[Manish Jethani, 2018-06-13 06:26:51]

I ran this test on Node.js v8.9.1, Chrome Canary (69), and Firefox 59:

  (function()
  {
    let array = new Array(10000000);
    for (let i = 0; i < 10000000; i++)
      array[i] = Math.random() < .5 ? {} : undefined;

    let s = Date.now();
    let n = 0;
    for (let i = 0; i < 10000000; i++)
      if (typeof array[i] != "undefined")
      //if (array[i] != null)
        n++;
    console.log(Date.now() - s, n);
  })();

The performance is about the same for `typeof array[i] != "undefined"` vs.
`array[i] != null` on both Chrome and Firefox. On Node.js v8.9.1 (V8
6.1.534.47), the latter is only slightly faster (~1-4%). So it looks like this
doesn't matter for browser-based stuff.

Sergei, if you think this helps for libadblockplus, we can make the change, but
otherwise I'll close this.