phpseclib: guardrails needed on isPrime and randomPrime

Impact Anyone trying to generate a prime and testing the primality of a number. Patches https://github.com/phpseclib/phpseclib/commit/ad5dbdf2129f5e0fb644637770b7f33de8ca8575 Workarounds Using the GMP extension would probably help, assuming that one has its own guardrails. Resources...