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!
Why not remove this and use a couple of vprint_error/print_error in check itself?  That way the check method gives an accurate explanation of why it made the finding it did and exploit can take advantage of it.