fix: err not updated after OTP authentication

[idawnlight]

Previously, err was not updated after client.AuthSMSCode(smsCode) or client.AuthTOTP(TOTPCode). As a result, even after successful authentication, the code would still panic at core/EasyConnectClient.go#L118:

    // check error after trying best server
    if err != nil {
        log.Fatal(err.Error())
    }