Add some small fixes to the MQAC local exploit

This PR piggybacks on to @zeroSteiner's great work on the MQAC local exploit.

* Add a check for `INVALID_HANDLE_VALUE` when attempting to open the device, as this is what is returned when the device doesn't exist (ie. when MSMQ is not installed).
* Make sure that we only run the exploit against targets that we support directly to make sure we don't BSOD machines (such as what happens with SP1/SP2).
* Add a call to `check` in the exploit code to cover all bases.

Minor fixes really, just to make sure that we don't lose boxes when running the sploit. Cheers!
minor, but use single quotes unless you are using interpolation or other thing that requires ".  msftidy should (now) be warning you about this.