CID 1321953 Assert in case GetTokenInformation is not returning ERROR_INSUFFICIENT_BUFFER

CID 1321953
GetTokerInformation should set last error to ERROR_INSUFFICIENT_BUFFER when called with dwlength=0;

The only value expected is this one, so Assert in case it sets a different one. The original if check is kept for extra-safeness, but I think it could be removed without any issues.