Make silent the overflow report for xorshift1024star calculation

[thsfs]

Got an UBSan error report from Address Sanitizer when running it upon core_test.

/ws/nano-node/nano/node/xorshift.hpp:18:12: runtime error: left shift of 3860899979500397099 by 31 places cannot be represented in type 'uint64_t' (aka 'unsigned long')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /ws/nano-node/nano/node/xorshift.hpp:18:12 in 

The overflow is expected as part of the calculation, but this should ideally not trigger an error.

Code portion from which the complain comes from:

class xorshift1024star final
{
public:
	std::array<uint64_t, 16> s;
	unsigned p{ 0 };
	uint64_t next ()
	{
		auto p_l (p);
		auto pn ((p_l + 1) & 15);
		p = pn;
		uint64_t s0 = s[p_l];
		uint64_t s1 = s[pn];
		s1 ^= s1 << 31; // a
		s1 ^= s1 >> 11; // b
		s0 ^= s0 >> 30; // c
		return (s[pn] = s0 ^ s1) * 1181783497276652981LL;
	}
};

OS: Ubuntu 20.04