Random numbers should not be produced using `rng() % max`.

[iphydf]

Modulus creates a bias towards smaller numbers.

[iphydf]

We need a uint32_t random_range(uint32_t min, uint32_t max); and replace the uses of random-modulo with it.

[JFreegman]

Libsodium's randombytes_uniform should be used https://libsodium.gitbook.io/doc/generating_random_data

[robinlinden]

Fixed in #1975.