Resolver: report SRV resolve failure if all A resolves failed. Previously, if an SRV record was successfully resolved, but all of its A records failed to resolve, NXDOMAIN was returned to the caller, which is considered a successful resolve rather than an error. This could result in losing the result of a previous successful resolve by the caller. Now NXDOMAIN is only returned if at least one A resolve completed with this code. Otherwise the error state of the first A resolve is returned.