Introduce operator+= to simplify response creation.

src/server/internalServer.cpp

@@ -633,12 +633,13 @@ std::unique_ptr<Response> InternalServer::handle_search(const RequestContext& re
       // Searcher->search will throw a runtime error if there is no valid xapian database to do the search.
       // (in case of zim file not containing a index)
       const auto cssUrl = renderUrl(m_root, RESOURCE::templates::url_of_search_results_css);
-      return HTTPErrorHtmlResponse(*this, request, MHD_HTTP_NOT_FOUND,
-                                   "fulltext-search-unavailable",
-                                   "404-page-heading",
-                                   cssUrl)
-           + nonParameterizedMessage("no-search-results")
-           + TaskbarInfo(searchInfo.bookName, archive.get());
+      HTTPErrorHtmlResponse response(*this, request, MHD_HTTP_NOT_FOUND,
+                                     "fulltext-search-unavailable",
+                                     "404-page-heading",
+                                     cssUrl);
+      response += nonParameterizedMessage("no-search-results");
+      response += TaskbarInfo(searchInfo.bookName, archive.get());
+      return response;
     }