Fix issue with kitrap0d crashing meterpreter

Calling getsystem or getsystem -t 4 was resulting in crashes due to
an incorrect usage of sizes in a call to _sprintf_s in the kitrap0d
code. This might have come about as a result of a move to the new
compiler which is C++11.

This code forces the size check to be correct and results in the
exploit functioning correctly on all platforms.