fix: prevent panic in getHostByName on DNS lookup failure

[Yanhu007]

Partially addresses #473 (Finding 3: CWE-476)

Problem

getHostByName discards the error from net.LookupHost and unconditionally indexes into the result slice:

func getHostByName(name string) string {
    addrs, _ := net.LookupHost(name)
    //TODO: add error handing when release v3 comes out
    return addrs[rand.Intn(len(addrs))]
}

When DNS resolution fails (e.g. NXDOMAIN, network error), addrs is nil, and rand.Intn(0) panics with an unrecoverable crash. The TODO comment acknowledges this was supposed to be fixed.

Fix

Check for errors and empty results. Return the input hostname unchanged when lookup fails, instead of panicking:

func getHostByName(name string) string {
    addrs, err := net.LookupHost(name)
    if err != nil || len(addrs) == 0 {
        return name
    }
    return addrs[rand.Intn(len(addrs))]
}

Testing

All tests pass (one pre-existing timezone-dependent failure in TestHtmlDate is unrelated).