fix(curl_thread_pool): clean up clients_in_proc in destroy()

destroy() aborted and deleted clients in the queue but did not
delete clients that were currently being processed (clients_in_proc).
If a thread was terminated while processing a client, that client
object and its CURL handle were leaked.

libs/http_client/curl_thread_pool_p.cpp

@@ -92,5 +92,10 @@ void CurlThreadPool::destroy() {
 		for (auto c: *cr)
 			delete c;
 	}
+	{
+		auto cr = clients_in_proc.getRef();
+		for (auto c: *cr)
+			delete c;
+	}
 	// piCout << "~CurlThreadPool ok";
 }