pselect6 with NULL {sigmask*,masksize} struct for 6th + 7th args does not work?

Created by: egrimley

This program does not seem to run correctly under DynamioRIO:

#include <sys/select.h>
#include <sys/syscall.h>
#include <unistd.h>

int main()
{
  fd_set fds;
  struct timespec ts;

  FD_ZERO(&fds);
  ts.tv_sec = 2;
  ts.tv_nsec = 0;
  return syscall(SYS_pselect6, 0, 0, 0, &fds, &ts, 0);
}

I think it's because the pselect6 code in pre_system_call does not check for the sigmask parameter being NULL.