[C++][Pistache] Compile error when nesting references (#16711) (#18586)

When components/schema/<object> reference other objects, validate() was
getting called on the referenced objects with no arguments. The return
value was void, but checked as if it was a boolean value.

samples/server/petstore/cpp-pistache-nested-schema-refs/api/StoreApi.cpp

@@ -0,0 +1,86 @@
+/**
+* Test swagger file
+* No description provided (generated by Openapi Generator https://github.com/openapitools/openapi-generator)
+*
+* The version of the OpenAPI document: 1.0.0
+* 
+*
+* NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+* https://openapi-generator.tech
+* Do not edit the class manually.
+*/
+
+#include "StoreApi.h"
+#include "Helpers.h"
+
+namespace org::openapitools::server::api
+{
+
+using namespace org::openapitools::server::helpers;
+using namespace org::openapitools::server::model;
+
+const std::string StoreApi::base = "";
+
+StoreApi::StoreApi(const std::shared_ptr<Pistache::Rest::Router>& rtr)
+    : ApiBase(rtr)
+{
+}
+
+void StoreApi::init() {
+    setupRoutes();
+}
+
+void StoreApi::setupRoutes() {
+    using namespace Pistache::Rest;
+
+    Routes::Get(*router, base + "/pet", Routes::bind(&StoreApi::get_nested_object_handler, this));
+
+    // Default handler, called when a route is not found
+    router->addCustomHandler(Routes::bind(&StoreApi::store_api_default_handler, this));
+}
+
+std::pair<Pistache::Http::Code, std::string> StoreApi::handleParsingException(const std::exception& ex) const noexcept
+{
+    try {
+        throw;
+    } catch (nlohmann::detail::exception &e) {
+        return std::make_pair(Pistache::Http::Code::Bad_Request, e.what());
+    } catch (org::openapitools::server::helpers::ValidationException &e) {
+        return std::make_pair(Pistache::Http::Code::Bad_Request, e.what());
+    } catch (std::exception &e) {
+        return std::make_pair(Pistache::Http::Code::Internal_Server_Error, e.what());
+    }
+}
+
+std::pair<Pistache::Http::Code, std::string> StoreApi::handleOperationException(const std::exception& ex) const noexcept
+{
+    return std::make_pair(Pistache::Http::Code::Internal_Server_Error, ex.what());
+}
+
+void StoreApi::get_nested_object_handler(const Pistache::Rest::Request &, Pistache::Http::ResponseWriter response) {
+    try {
+
+
+    try {
+        this->get_nested_object(response);
+    } catch (Pistache::Http::HttpError &e) {
+        response.send(static_cast<Pistache::Http::Code>(e.code()), e.what());
+        return;
+    } catch (std::exception &e) {
+        const std::pair<Pistache::Http::Code, std::string> errorInfo = this->handleOperationException(e);
+        response.send(errorInfo.first, errorInfo.second);
+        return;
+    }
+
+    } catch (std::exception &e) {
+        response.send(Pistache::Http::Code::Internal_Server_Error, e.what());
+    }
+
+}
+
+void StoreApi::store_api_default_handler(const Pistache::Rest::Request &, Pistache::Http::ResponseWriter response) {
+    response.send(Pistache::Http::Code::Not_Found, "The requested method does not exist");
+}
+
+} // namespace org::openapitools::server::api
+