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.
Updated fix to work properly with _snprintf_s

* Modified first and second parameters to use `dwOutputLength` which
  is given to the function as an indicator of buffer size in bytes
  anyway.
* Check the return value of the function call to see if the result
  was a truncation, and if so, break from the current loop.

Realistically, truncation will not happen because the default windows
installation location folder name is very short.

Thanks @jvazquez-r7 for prodding me to validate this.
Last code tidy for the kitrap0d fix

Tidies up the API to be more intuitive, including conversion of the
first parameter to a char pointer (removing MAX_PATH) and renaming
the second parameter to be more indicative of what it means.

Thanks to @jvazquez-r7 for the great discussion!
Land #23, @OJ's fix for kitrap0d