[HttpClient] fix reading the body after a ClientException

Author: nicolas-grekas

Test/Fixtures/web/index.php

@@ -66,6 +66,9 @@
     case '/404-gzipped':
         header('Content-Type: text/plain', true, 404);
         ob_start('ob_gzhandler');
+        @ob_flush();
+        flush();
+        usleep(300000);
         echo 'some text';
         exit;