Close body after error check

Otherwise it panics for nil body

pkg/notifications/slack/slack.go

@@ -29,10 +29,10 @@ func NotifyReboot(hookURL, username, nodeID string) error {
 	}
 
 	resp, err := httpClient.Post(hookURL, "application/json", &buf)
-	defer resp.Body.Close()
 	if err != nil {
 		return err
 	}
+	defer resp.Body.Close()
 
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 		return fmt.Errorf(resp.Status)