Fix pointer truncation during process iteration

![64 bits](http://i.imgur.com/ssjxQjy.jpg)

In similar vein to the migration issue, incognito was crashing when running under SYSTEM processes (such as lsass.exe). This was because of a pointer truncation problem when processes were being enumerated. The line causing the issue was [this one here](https://github.com/OJ/meterpreter/commit/57d8ee85d977b73113abcc15b31cd8c306b62582#diff-235c3eddd9cbb1eeed89a31295d8bd24R358).

There was also some other quirky logic going on, but nothing too damaging. I added some other simple code tidies while I was in there.

I stumbled on this while testing something for a friend. I hate crashes, so didn't want to wait until Wednesday to see it fixed.

[SeeRM #8739]