Add checks for RNG seed values

[laprej]

From "A random number generator based on the combination of four LCGs" by L'Ecuyer and Andres, all seed values must satisfy "1 <= s[0] <= 2147483646, 1 <= s[1] <= 2147483542, 1 <= s[2] <= 2147483422, 1 <= s[3] <= 2147483322."

We need to add checks that maintain this invariant.