fix - agent.Struct fails to unmarshal response since 2.33.0 #2134 (#2137)

client.go

@@ -826,6 +826,10 @@ func (a *Agent) Struct(v interface{}) (code int, body []byte, errs []error) {
 		return
 	}
 
+	if a.jsonDecoder == nil {
+		a.jsonDecoder = json.Unmarshal
+	}
+
 	if err := a.jsonDecoder(body, v); err != nil {
 		errs = append(errs, err)
 	}