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 addtime(struct timeval *a, struct timeval *b)
{
	timeradd(a, b, b);
}

void addtime(struct timeval *a, struct timeval *b)
{
	timeradd(a, b, b);
}
