Avoid integer overflow in delay calculation.

  /* How much are we willing to add to the delay? */

  int max_increment;

  const int multiplier = 4; /* no more than quintuple. */

  if (delay)

    max_increment = delay * 4; /* no more than quintuple. */

  else

  if (delay && delay < (INT_MAX-1) / multiplier) {

    max_increment = delay * multiplier;

  } else if (delay) {

    max_increment = INT_MAX-1;

  } else {

    max_increment = 1; /* we're always willing to slow down a little. */

  }

  /* the + 1 here is so that we include the end of the interval */

  int increment = crypto_rand_int(max_increment+1);