stratum: parse_notify(): Don't die on malformed bbversion/prev_hash/nbit/ntime.

Might have introduced a memory leak, don't have time to check. :(

Should the other hex2bin()'s be checked?

Thanks to Mick Ayzenberg <mick.dejavusecurity.com> for finding this.
void cgtimer_sub(cgtimer_t *a, cgtimer_t *b, cgtimer_t *res)
{
	res->tv_sec = a->tv_sec - b->tv_sec;
	res->tv_nsec = a->tv_nsec - b->tv_nsec;
	if (res->tv_nsec < 0) {
		res->tv_nsec += 1000000000;
		res->tv_sec--;
	}
}

void cgtimer_sub(cgtimer_t *a, cgtimer_t *b, cgtimer_t *res)
{
	res->tv_sec = a->tv_sec - b->tv_sec;
	res->tv_nsec = a->tv_nsec - b->tv_nsec;
	if (res->tv_nsec < 0) {
		res->tv_nsec += 1000000000;
		res->tv_sec--;
	}
}
