Since `random(x)` returns a random number in [0,x), it will always output a number that is less than `x` (the initial value of x is 1 in this case). Therefore, the outcome where repeated applications of `random(...)` to its own result has little shrinking effect is vanishingly small. It's the result of these repeated applications that is being subtracted from the length of the unit vector that is used to position each pixel. So the pixels naturally accumulate around that unit length. No broken crypto here.

It's sort of like asking, "What would happen if I multiply a bunch of numbers together that are guaranteed to be less than 1 (and even much less than 1 much of the time)?"